Casting a wider fish net on animal models in ...

PNP-08589; No of Pages 9 Progress in Neuro-Psychopharmacology & Biological Psychiatry xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Progress in Neuro-Psychopharmacology & Biological Psychiatry journal homepage: www.elsevier.com/locate/pnp

Casting a wider fish net on animal models in neuropsychiatric research Zachary J. Hall a,1, Alex R. De Serrano b,1, F. Helen Rodd b,⁎, Vincent Tropepe a,⁎⁎ a b

Department of Cell & Systems Biology, University of Toronto, Canada Department of Ecology & Evolutionary Biology, University of Toronto, Canada

a r t i c l e

i n f o

Article history: Received 18 February 2014 Received in revised form 28 March 2014 Accepted 1 April 2014 Available online xxxx Keywords: Behavior Brain Guppy Zebrafish Neurodevelopment

a b s t r a c t Neuropsychiatric disorders, such as schizophrenia, are associated with abnormal brain development. In this review, we discuss how studying dimensional components of these disorders, or endophenotypes, in a wider range of animal models will deepen our understanding of how interactions between biological and environmental factors alter the trajectory of neurodevelopment leading to aberrant behavior. In particular, we discuss some of the advantages of incorporating studies of brain and behavior using a range of teleost fish species into current neuropsychiatric research. From the perspective of comparative neurobiology, teleosts share a fundamental pattern of neurodevelopment and functional brain organization with other vertebrates, including humans. These shared features provide a basis for experimentally probing the mechanisms of disease-associated brain abnormalities. Moreover, incorporating information about how behaviors have been shaped by evolution will allow us to better understand the relevance of behavioral variation to determine their physiological underpinnings. We believe that exploiting the conservation in brain development across vertebrate species, and the rich diversity of fish behavior in lab and natural populations will lead to significant new insights and a holistic understanding of the neurobiological systems implicated in neuropsychiatric disorders. © 2014 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Shifting focus to endophenotypes and comparative studies . . . . . . . . . . . . . . . . . . . . . . . . . 3. Using fish to understand the neurobiological substrates of behavior . . . . . . . . . . . . . . . . . . . . . 4. Gaining insights into the neurodevelopmental origins of psychiatric disorders using zebrafish . . . . . . . . . . . 5. The Trinidadian guppy as an emerging model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Studying the role of maternal environment on brain and behavioral development in guppies and related species. 7. Summary and outlook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction Neuropsychiatric disorders are characterized by life-long cognitive and behavioral impairments with severe effects on quality of life. A

Abbreviations: GABAergic, Gamma-amino buytaric acid producing neurons; RNA, ribonucleic acid; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. ⁎ Correspondence to: H. Rodd, Department of Ecology & Evolutionary Biology, University of Toronto, 25 Harbord Street, Toronto, ON M5S 3G5, Canada. Tel.: +1 416 946 5035. ⁎⁎ Correspondence to: V. Tropepe, Department of Cell & Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON M5S 3G5, Canada. Tel.: +1 416 946 0338. E-mail addresses: [email protected] (F.H. Rodd), [email protected] (V. Tropepe). 1 Equal contribution.

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

0 0 0 0 0 0 0 0 0

substantial proportion of adults with these disorders can begin exhibiting symptoms while they are relatively young, indicating that a better understanding of the origins of neuropsychiatric illness requires a focus on mechanisms of brain and behavioral development (Money and Stanwood, 2013). This is especially critical because symptoms of disease often manifest long after underlying causal processes have initiated. Neuropsychiatric disorders are often associated with genetic and environmental perturbations during critical periods in brain development (Jaffee and Price, 2007). Thus, the challenge is to understand how interactions between genetic, epigenetic and environmental factors alter the trajectory of neurodevelopment to produce the aberrant structural and biochemical changes in the brain that are characteristic of disease. To improve therapeutic outcomes, we need to learn how to redirect maladaptive developmental trajectories toward a more typical

http://dx.doi.org/10.1016/j.pnpbp.2014.04.003 0278-5846/© 2014 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Please cite this article as: Hall ZJ, et al, Casting a wider fish net on animal models in neuropsychiatric research, Prog Neuro-Psychopharmacol Biol Psychiatry (2014), http://dx.doi.org/10.1016/j.pnpbp.2014.04.003

2

Z.J. Hall et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry xxx (2014) xxx–xxx

path. Animal models that enable us to easily manipulate genes and the environment could teach us to detect when structural and biochemical changes occur in the brain during development and to determine how they might be corrected. For decades, studies on the causes and treatment of neuropsychiatric disorders have relied mostly on a few, intensively studied, rodent lab species. Therapeutic interventions discovered using these animal models have not always been easily transferred to humans. For example, whereas learning deficits in one genetic mouse model of neurofibromatosis type 1 were rescued with administration of statins, participants in a subsequent human clinical trial using the same therapy showed no significant improvement on any learning measures employed (Castrén et al., 2012; Krab et al., 2008). Despite the impressive progress towards developing animal (especially rodent) models, it is clear that these models do not capture the full complexity of human mental illness. Limitations in the cross-species transferability in neuropsychiatric interventions stem from: (1) a historic focus on an attempt to recreate complete neuropsychiatric disorders, as they are identified in humans, in lab models; and (2) a disproportionate understanding of how dysfunctional neurobiological substrates produce neuropsychiatric symptoms in only a few model species. In this review, we discuss how a paradigm shift from trying to recreate full neuropsychiatric disorders in a single species to studying dimensional components of these disorders, or endophenotypes, will be extremely productive and allow the use of additional species for research. We specifically discuss some of the advantages of incorporating studies of brain and behavioral development using various fish species into current neuropsychiatric research. Furthermore, we address the suitability of fish as potential lab models from both a comparative neurodevelopmental and neuroethological perspective.

2. Shifting focus to endophenotypes and comparative studies Recreating the constellation of genetic (e.g., heritable polymorphisms or de novo mutations) and environmental (e.g., social interactions, nutrition) factors contributing to neuropsychiatric disorders in lab animals to produce bona fide disease models has been challenging. Instead of modeling all aspects of a disorder, focus has shifted toward using animals to model endophenotypes, which are heritable traits with clear, quantifiable, and neurobiological connections to a disorder that has been identified in humans (Bearden and Freimer, 2006; Gottesman and Gould, 2003). Endophenotypes are often considered intermediate neurobiological phenotypes that mediate genetic and environmental effects to produce behavioral and cognitive symptoms in neuropsychiatric disorders (Reus and Freimer, 1997). Unlike many current neuropsychiatric diagnostic criteria, which are criticized for relying on qualitative, discrete symptoms to classify disease and failing to capture variation in the expression of disease among individuals (Hyman, 2010), endophenotypes are often quantifiable and continuous. Accordingly, the National Institute of Mental Health has moved toward the incorporation of endophenotypic data in neuropsychiatric diagnosis by establishing the Research Domain Criteria Matrix framework. This matrix summarizes endophenotypes on all levels of mechanism from genes to behavior for mental health disorders. Among endophenotypes, alterations in brain structure, gene expression, and neurotransmitter signaling are now easily investigated across vertebrate species because of significant conservation in the cellular mechanisms of brain development. For example, endophenotypes of schizophrenia include impaired dopaminergic and GABAergic signaling (reviewed in Souza and Tropepe, 2011). On the other hand, behavioral and cognitive endophenotypes are more challenging to investigate because they rely heavily on behavioral paradigms not adapted for testing non-traditional lab species. For example, negative mood, a cognitive endophenotype of depression, is often sampled in rodents using forced swim tests (Homberg, 2013), which pose clear challenges with cross-species comparison to other taxa such as fish.

The recent shift in emphasis to modeling endophenotypes for neuropsychiatric research has three major benefits. First, endophenotypes provide a biological description of symptoms that can be accurately quantified in non-human animals, such as GABAergic neuronal population size and connectivity, or elevated dopamine receptor expression. Second, using endophenotypes avoids potential problems with anthropomorphic paradigm design and interpretation of animal behavior when models are treated as bona fide recreations of human disorders. For example, Homberg (2013) describes the controversial interpretation of depressive immobility in rats placed in an inescapable stressful situation, the Porsolt swim test. In this test, a rat is placed in a pool of water from which it is impossible to escape and the time to which the rat ceases to try to escape and begins treading water is measured. Historically, treading water in this test is interpreted as negative mood or helplessness, although, as Homberg (2013) explains, this behavior may actually reflect an adaptive, presumably energetically favorable, response to chronic stress that indicates how the animal copes with the challenge. Third, a focus on neurobiologically defined endophenotypes affords us the opportunity to expand the repertoire of animal models to other species in which these endophenotypes can be easily observed and manipulated. Specifically, we suggest that a productive approach to studying endophenotypes in animal models is to first describe neural systems and the associated set of normal behaviors they support. These brain–behavior relationships are often originally established using functional neuroscience to correlate neuronal activity with production of a behavior and confirmed by establishing a causal brain–behavior relationship by manipulating neuronal signaling in this pathway and testing for subsequent effects on the behavior of interest. Second, we can test how these brain–behavior patterns compare across species, like the work that has been conducted on the conserved social decision-making circuit, a neural circuit in the basal forebrain and midbrain that appears to mediate social interaction behavior in vertebrates (O'Connell and Hofmann, 2011). Third, we can compare how alterations in conserved brain–behavior relationships compare to endophenotypes associated with cognitive and behavioral impairment. Finally, we stress the importance of validating behavioral tests for each species before using them to make behavioral inferences, as natural history and ecological differences between species can affect the usefulness of said tests. Validation can be thought of as ensuring that the behavioral assay actually represents the theoretical definition of that behavior (Cozby, 1997). Empirical tests of behavioral consistency will help determine how well a test appears to measure the behavioral variable in question. For example, this process has been used to validate the open field test as an assay for exploratory behavior in guppies (Burns, 2008). A similar approach has been applied to larval zebrafish where assessment of individual behavioral variation within a population allowed for a separation of the different types of responders to examine baseline movement and how this movement changed as a result of alterations in neuromodulator signaling (Shamchuk and Tierney, 2012). This approach allows us to take advantage of the burgeoning field of neuroethology, which identifies the neural substrates supporting the production of naturally occurring animal behavior, including individual variation. Here we argue that ongoing neurobiological, genetic, and ethological work has set the stage for the increased use of fish in neuropsychiatric model organism research. By incorporating endophenotypes, new animal models, and comparative studies into neuropsychiatric research, we believe that we can achieve new insight and holistic understanding of the neurobiological systems implicated in neuropsychiatric disorders. 3. Using fish to understand the neurobiological substrates of behavior Current neuropsychiatric models are almost entirely limited to the use of pharmacologically- and genetically-manipulated rodents. The use of rodent animal models of disease is often justified because of a



common mammalian ancestry with humans and neuroanatomical homology for most of the brain (Parker and Brennan, 2012). Several genetic manipulation techniques are also available for mice and, more recently, rats (Wöhr and Scattoni, 2013). In addition to rodent models, recent work has promoted the use of genetically manipulated Drosophila to study neuropsychiatric disorders (O'Kane, 2011). Use of these insects promises simplified neuroanatomy and behavioral scoring, and also huge increases in scale of operation and genetic tractability. A deep homology between invertebrate and vertebrate anterior brain structures has been proposed, especially at the levels of neuronal differentiation and basic organization of sensory–neurosecretory versus motor neuronal organization (Strausfeld and Hirth, 2013). Nonetheless, the comparatively reduced structural complexity and lack of vertebratespecific homologies between invertebrates and humans poses a challenge for modeling brain systems that might be relevant to human disease. We believe that fish provide a useful balance between these two systems for studying neuropsychiatric endophenotypes within and between species, especially where we can take advantage of experimentally tractable species and understand behavior in both the lab and natural populations. Fish provide an array of practical benefits as a lab model. Fish models provide the opportunity for a substantial increase in the scale of experimental operation compared to rodents, enabling large-scale behavioral and genetic screens and rapid study of the effects of pharmacological and genetic perturbations during development (Pickart and Klee, 2014). Indeed, studies using a wide range of fish species have begun to characterize dopaminergic and serotonergic brain systems (see Table 1). Despite some interspecific differences in protein/RNA expression, general patterns are observed across teleosts. For example, tyrosine hydroxylase (TH; an enzyme in the dopamine synthesis pathway) expression shows consistent general patterns throughout the forebrain, although there are minor differences between species in withinstructure expression, including differences in the number of THpositive nuclei in the ventral telencephalon. An exciting future avenue of research will be to link these relatively small neurological differences in closely related species to ecological variation and behavioral phenotypes to establish robust endophenotypes. Although the teleost pallium lacks a characteristic laminar organization, which is observed in the cerebral cortex of mammals, it nonetheless contains nuclear masses with distinct afferent and efferent circuitry that resemble a rudimentary cortical organization (Ito and Yamamoto, 2009). Moreover, our understanding of many basal neurotransmitter systems implicated in neuropsychiatric disorders, including

3

dopaminergic, serotonergic, and noradrenergic (e.g., McLean and Fetcho, 2004; Table 1) circuitry in fish is providing mounting evidence for anatomical, hodological, and neurochemical conservation in these circuits with mammals, including humans (O'Connell and Hofmann, 2012; Panula et al., 2006). This conservation is further supported by the observation of similarities in the inverted-U shaped dopamine receptor response kinetics (attributed to differential binding affinities for D1 and D2 receptors), which has been observed in mammals and now replicated in zebrafish (Souza et al., 2011; Williams and Castner, 2006). Over the past decade, zebrafish have become one of the most genetically tractable animal species for modeling human disease (Pickart and Klee, 2014). Many of these techniques, such as transgenics and targeted mutagenesis, are now being used in other fish species as well. With the current availability of genomic and transcriptomic databases for zebrafish (Howe et al., 2013; Vesterlund et al., 2011), medaka (Berger, 2010; Kasahara et al., 2007), sticklebacks (Jones et al., 2012; Leder et al., 2009), guppies (Fraser et al., 2011), and tilapia (ongoing; Lee et al., 2010), fish are rapidly becoming the best vertebrate model for studying the effects of genetic manipulation across diverse genetic backgrounds encompassing multiple strains and species. In addition to these practical benefits, studying fish affords us the opportunity to compare the function of neurobiological systems in lab strains with those in/from natural populations. Because brains have evolved to integrate sensory information and respond to environmental stressors, often in a species- or population-specific manner, there has been increasing pressure to incorporate ethology into behavioral neuroscience in non-human animals (Smulders, 2009; Stewart and Kalueff, in press). Even within Rodentia, variation in the organization of primary sensory and motor cortices is likely associated with species-specific differences in perception and behavior (Krubitzer et al., 2011); however, this variation has been neglected in standardized lab paradigms. Furthermore, studying natural populations provides the ecological and evolutionary context needed to fully interpret the function of, and understand variation in, behavioral phenotypes. Focusing on ethology takes advantage of naturally occurring behaviors that often come with clear motivations, such as courtship, and that have evolved to meet the demands of the animal's environment (including interactions with conspecifics). Although model organisms are desirable because of their standardized genetic background and ease of care in the lab, these very qualities can also lead to potential problems in the interpretation of behavior. By rearing generations of organisms in the lab, we may unknowingly select

Table 1 Examples of teleostean species in which neurotransmitter systems have been characterized. DOPAC: DA metabolite (3,4-dihydroxyphenylacetic acid); DBH: dopamine beta-hydroxylase; TH: tyrosine hydroxylase; 5-HTP: (serotonin precursor) 5-hydroxytryptophan; TPH = tryptophan hydroxylase; IHC: immunohistochemistry; ISH: in situ hybridization.

Dopamine (DA)

Species

Characterization

Representative reference

Bass, Dicentrarchus labrax Cichlid, Astatotilapia burtoni

5-HT, DA, L-DOPA, TH, DBH, phenylethanolamine N-methyl transferase [IHC] TH, D1a, D2 receptors [IHC] DA cell group gene expression DA and DOPAC levels during feeding and migratory stages TH [IHC] Aromatic L-amino acid decarboxylase [IHC] DBH [IHC] TH, DBH [IHC] DA in pituitary [IHC] Dopa decarboxylase [GFP reporter assay] DA (D2R) [ISH] TH [IHC and ISH] DA, TH, DBH [IHC] TH [IHC] TH [IHC] 5-HT [receptor binding assay] 5-HT [IHC] TPH mRNA, TPH [IHC], 5-HT and 5-HTP levels 5-HT [IHC]

Batten et al. (1993) O'Connell et al. (2011) O'Connell et al. (2013) Giorgi et al. (1994) Parafati et al. (2009) Beltramo et al. (1994) Hornby and Piekut (1988) Hornby and Piekut (1990) Kah et al. (1986) Fujimori (2009) Vacher et al. (2003) Vetillard et al. (2002) Ekstrom et al. (1992) Marsh et al. (2006) McLean and Fetcho (2004) Winberg and Nilsson (1996) Batten et al. (1993) Raghuveer et al. (2011) McLean and Fetcho (2004)

European eel, Anguilla anguilla Guppy, Poecilia reticulata Goldfish, Carassius auratus

Medaka, Oryzias latipes Rainbow trout, Oncorhynchus mykiss

Serotonin (5-HT)

Stickleback, Gasterosteus aculeatus Wrasse, Thalassoma bifasciatum Zebrafish, Danio rerio Arctic charr, Salvelinus alpinus Bass, Dicentrarchus labrax Catfish, Clarias gariepinus Zebrafish, Danio rerio


4


for traits that are adaptive for living in a lab environment (e.g. McGrath et al., 2009), including a reduced fear of ‘predators’ and a reduced ability to adjust to dynamic conditions, both of which can have neurophysiological implications. Similarly, selection against less fit variants can be weak or absent in controlled lab environments, potentially leading to a buildup of deleterious alleles or combinations of alleles that would not normally occur in natural populations. This, in combination with reduced genetic variation due to founder effects and inbreeding in lab populations, suggests that neurobehavioral responses may not be representative of those expressed by natural populations. In support of this, a meta-analysis across taxa demonstrated that inter-individual behavioral differences in aggression, boldness, and exploratory behavior are more consistent over time in field organisms than in lab organisms (Bell et al., 2009). Although the mechanism underlying this apparent reduction in the cohesiveness of behavior types across lab animals' lifespans has yet to be identified, the finding suggests that some aspect of the lab environment disrupts these adaptively linked behaviors. Another concern when studying lab-adapted species is that a behavioral response observed in the lab may not be biologically relevant in the natural environment, especially for behavioral phenotypes that depend on the environment in which they evolved. For example, lab animals may show reduced aggression to conspecifics both because of selection for this phenotype in the lab and because they were reared under nonstressful conditions in the lab (e.g., high food availability, with docile individuals). On the other hand, comparing individuals that have been lab-reared to those caught from natural populations provides an opportunity to examine how experience can significantly alter behavior. An example of this is found in studies showing differences between fieldcaught (predator-experienced) versus lab-reared (predator-naïve) female Atlantic mollies in their mate preferences in the presence of natural predators (Bierbach et al., 2011). Incorporating information about how behaviors have been shaped by evolution will allow us to better understand the relevance of behavioral variation, and natural variants offer a broader array of phenotypes to study and determine their physiological underpinnings. In fish, much is already known about the neurobiology of natural behavior and how individuals can change their behavior to respond to stressors in the natural environment (Brown et al., 2011). For example, neural substrates underlying many behaviors, including aggression, dominance, and affiliation, have been identified in cichlids (Greenwood et al., 2008; Oldfield and Hofmann, 2011; Trainor and Hofmann, 2006), zebrafish (Colman et al., 2009; Larson et al., 2006), blenniid fish (Grober et al., 2002), and species in the family Salmonidae (Øverli et al., 1999; Winberg and Nilsson, 1992, 1993), among many others (Table 2). It has been suggested that the brain regions responsible for social behavior and the reward pathway (and their integration) were present in primitive vertebrates (O'Connell and Hofmann, 2011). As such, mammals and fish share an ancient, but conserved neural circuitry underlying social behaviors (and likely non-social, rewarding behaviors as well), so it is perhaps not surprising that many types of social behavior elicit similar physiological responses across taxa. For example, although not explicitly measured for comparative purposes, some endocrine and behavioral responses to stressful social situations in fish appear to be congruent with responses to similar situations in rodents. Specifically, the social defeat paradigm (where individuals are forced to retreat in social encounters) is often used to induce a depressive-like state in rodents, which includes changes in behavior (reduced social interaction, anhedonia) and in endocrine response (elevation of the hypothalamic–pituitary axis (HPA), altered endocrine metabolism) that mirror symptoms of depression in humans (e.g. Blanchard et al., 1993). In some species, notably the Salmonidae, dominance hierarchies form in which the subordinate individuals exhibit persistent, altered behavioral and endocrine responses following defeat (Abbott et al., 1985). Although proper validation is still required, at face value, these changes in behavioral inhibition and increased activity of the hypothalamic–pituitary–interrenal axis (the teleost homolog to the HPA; Øverli et al., 1999; Winberg and Lepage,

1998) appear to be similar to the changes observed in defeated rodents. Together, these findings provide evidence for a common response of fish and rodents to social stress, supporting the cross-taxa validity of this paradigm. Furthermore, new fish models of human psychiatric and neurological disease have shown tremendous promise. Petzold et al. (2009) developed assays to sample locomotor responses to nicotine exposure and sensitization for forward genetic screens in a zebrafish population with induced genetic variation. In addition to characterizing the development of nicotinic locomotor responses in wild-type zebrafish, the authors identified two zebrafish mutants with an altered nicotine response. Both mutations were localized to genes with human orthologs, potentially providing novel genetic targets for the study of nicotine addiction. Similar protocols have been used to isolate zebrafish mutants with altered sensitivity to ethanol (Peng et al., 2009). The degree to which locomotor sensitization in these studies reflects incentive sensitization, thought to be the hallmark cognitive endophenotype of substance addiction (Robinson and Berridge, 2008), requires additional testing. Matsui et al. (2013) created mutants with deficiencies in orthologs of genes associated with Parkinson's disease in humans. Fish that were deficient in two genes, pink1 and parkin, developed behavioral phenotypes similar to Parkinson's disease in humans, and showed subsequent degeneration of dopaminergic neurons and defects in mitochondrial enzymatic activity, both of which are endophenotypes associated with this disease. Finally, in studies of senescence, Reznick et al. (2004, 2006) examined the evolution of reproductive life history traits of wild populations of guppies, and found that increased extrinsic mortality rate (as a product of predation pressure) selects for longer lifespans by specifically lengthening the period in which individuals are capable of reproduction. This is the only vertebrate study to-date to provide a model in which the evolution and genetic basis of senescence, including age related behavioral performance, can be studied in an experimental paradigm. For these reasons, we believe that complementing studies of lab-adapted fish species with parallel studies of the neuroethology of fish from wild populations will provide a robust understanding of how the brain develops to control behavior across species. 4. Gaining insights into the neurodevelopmental origins of psychiatric disorders using zebrafish Although various neurotransmitter systems have been investigated in zebrafish (e.g., McLean and Fetcho, 2004), the dopaminergic system is perhaps the most widely studied so far and, for the purposes of this review, serves to exemplify how brain and behavior studies in fish are useful for modeling relevant disease endophenotypes. The distribution and organization of dopaminergic neuronal populations in zebrafish show striking similarity to those in mammals; this is attributed to conservation in inductive signaling and genetic processes controlling neurogenesis during brain development (reviewed in Souza and Tropepe, 2011; Tropepe and Sive, 2003). Furthermore, genetic and pharmacological perturbation to the development and function of dopaminergic neurons produces motor deficits in zebrafish akin to those observed in mammals, suggesting functional conservation in the affected dopaminergic circuit with the mesostriatal dopaminergic pathway in mammals (Dunnet, 2005; Souza and Tropepe, 2011). Based on this conserved development and function, Souza et al. (2011) tested the suitability of the zebrafish as a model of the neurodevelopmental and behavioral consequences of impaired dopaminergic signaling during development, a relevant endophenotype in schizophrenia (Hurd and Hall, 2005). The authors perturbed neurodevelopment in zebrafish larvae by altering dopaminergic signaling, which influences multiple neurogenic processes involved in dopaminergic neuronal development in fish and mammals (Souza and Tropepe, 2011) and GABAergic neuronal development in mammals (Crandall et al., 2007). Dopamine treatment was administered 3–5 days postfertilization; a sensitive period during which neurons are capable of responding to dopamine, but dopaminergic circuitry has not fully



5

Table 2 Examples of associations between dopamine (DA) or serotonin (5-HT) and ecologically-relevant behavior in teleostean species. DA: dopamine; DOPAC: DA metabolite (3,4-dihydroxyphenylacetic acid); 5-HT: serotonin; 5-HIAA: serotonin metabolite (5-hydroxyindoleacetic acid).

Dopamine (DA)

Species

Results

Representative reference

Arctic charr, Salvelinus alpinus

DA increased aggression, and aggressor became dominant DA decreased attack latency DA decreased food intake MPTP (neurotoxin) decreased movement; L-deprenyl (monoamine oxidase-B inhibitor) rescued movement Amphetamine decreased food intake MPTP (neurotoxin) decreased DA positive cells and caused locomotor dysfunction when given to larva, but not adults PINK1 and Parkin mutants had locomotor dysfunctions; decreased DA levels Predator exposure increased DA, followed by a decrease in DOPAC; conspecific intruder decreased DA followed by an increase in DOPAC DOPAC/DA higher in some brain regions of subordinate fish following hierarchy formation Apomorphine increased aggression D2 receptor activation during development reduced movement initiation in larvae; reduced number of GABAergic neurons 5-HIAA/5-HT showed long-term increase in subordinate individuals; only short-term (1 day) 5-HIAA increase in dominant individuals Fluoxetine increased time to capture prey; decreased 5-HT levels Fluoxetine increased time to capture prey; decreased 5-HT levels Serotonin decreased duration of displays; 8-OH-DPAT (5-HT1A receptor agonist) increased approach latency, decreased display duration; fluoxetine decreased 5-HT levels Fluoxetine decreased aggression but not courtship behavior Serotonin reduced food intake and latency to move in fingerling carp Serotonin reduced aggression 5-HIAA and 5-HIAA/5-HT ratios higher in territorial males; sexual maturation regulated by social interactions Exposure to predator increased 5-HIAA/5-HT ratio relative to controls Males and newly sex-changed fish had higher 5-HT/5-HIAA ratios, but levels were not affected by serotonin implants Citalopram had no effect on gonopodial thrusts Fluoxetine decreased aggression, and reduced swimming speed more/for longer duration than controls in juveniles Propranolol decreased number of visits to the nest by males, but didn't affect other reproductive behaviors Fluoxetine, sertraline, venlafaxine, bupropion caused no difference in sex characteristics or nest holding ability of males, but reduced survival, induced vitellogenin and altered testis morphology Decreased shelter seeking behavior in adult males Fluoxetine reduced locomotor activity Fluoxetine reduced locomotor activity Serotonin decreased in response to a conspecific intruder and a predator Citalopram did not affect aggressive behavior of fry 5-HIAA/5-HT higher in subordinate fish following hierarchy formation Fluoxetine decreased aggression in territorial males when confronted with intruders

Winberg and Nilsson (1992) Höglund et al. (2001) Leal et al. (2013) Adeyemo et al. (1993).

Bass, Dicentrarchus labrax Goldfish, Carassius auratus

Medaka, Oryzias latipes

Stickleback, Gasterosteus aculeatus Rainbow trout, Oncorhynchus mykiss

Zebrafish, Danio rerio Serotonin (5-HT)

Arctic charr, Salvelinus alpinus Bass, hybrid striped (Morone saxatilis × M. chrysops) Betta, Betta splendens

Carp, Cyprinus carpio Cichlid, Aequidens pulcher Cichlid, Haplochromis burtoni Damselfish, Pomacentrus partitus Goby, Lythrypnus dalli Guppy, Poecilia reticulata Killifish, Aphanius dispar Minnow, Pimephales promelas

Minnow, Cyprinodon variegatus Mosquitofish, Gambusia affinis Stickleback, Gasterosteus aculeatus Rainbow trout, Oncorhynchus mykiss Wrasse, Thalassoma bifasciatum

developed (Schweitzer and Driever, 2009) and several simple visuomotor behaviors first appear (Portugues and Engert, 2009). Through the use of pharmacological agents, the authors found that altered dopaminergic signaling caused significant reductions in both the development of GABAergic neuronal populations throughout the brain and in larval movement during behavioral assays following treatment. The authors demonstrated that these effects on GABAergic neuron development and locomotion are mediated through D2-receptor-mediated inhibition of Akt activity, as previously reported in rodents (Beaulieu et al., 2004, 2005, 2007). By incorporating treatments with the dopamine neurotoxin MPTP, the authors also demonstrated that reductions in GABAergic neuron development and locomotion are produced when dopaminergic signaling was agonized or antagonized, producing an inverted-U shape response curve characteristic of altered dopamine signaling in mammals (Souza et al., 2011; Williams and Castner, 2006). The similarity between mammals and zebrafish in the effects of altered dopaminergic signaling on neurodevelopment, behavior, and response kinetics show that it is appropriate to study altered dopaminergic signaling, in addition to these downstream effects on neuronal circuitry and locomotion, as endophenotypes across species. It is worth mentioning that animal models of GABAergic neuronal development, like the zebrafish, are

Volkoff (2013) Matsui et al. (2009) Matsui et al. (2013) Bell et al. (2007) Øverli et al. (1999) Tiersch and Griffith (1988) Souza et al. (2011) Winberg and Nilsson (1993) Bisesi (2011) (thesis) Gaworecki and Klaine (2008) Clotfelter et al. (2007)

Dzieweczynski and Hebert (2012) Kuz'mina and Garina (2013) Munro (1986) Winberg et al. (1997) Winberg and Nilsson (1993) Lorenzi et al. (2009) Holmberg et al. (2011) Barry (2012) Lorenzi et al. (2012) Schultz et al. (2011)

Valenti et al. (2012) Winder et al. (2012) Henry and Black (2007) Bell et al. (2007) Holmberg et al. (2011) Øverli et al. (1999) Perreault et al. (2003)

particularly attractive given recent work demonstrating that GABAergic circuit maturation determines the onset of critical periods in brain development (Takesian and Hensch, 2013). This recent finding, combined with a recent shift in therapeutic intervention to treating neurodevelopmental disorders in adulthood by reactivating neuroplasticity to levels observed in critical periods of development (Castrén et al., 2012), shows that zebrafish will be an invaluable model in future neuropsychiatric research. 5. The Trinidadian guppy as an emerging model The Trinidadian guppy, Poecilia reticulata, a small freshwater fish, is a powerful model system for the study of the evolution of morphological, life history and behavioral traits in a natural context (Houde, 1997; Magurran, 2005). Wild populations in Trinidad show substantial variation in many traits that have been shaped by both natural and sexual selection; this has functioned to create a large pool of known natural variation in phenotypes, which can be used for comparative studies. A key ecological factor that has influenced many traits of guppies is predation. Predators that co-occur with guppies impose different predation risks in different sections of streams and rivers. Guppies from ‘high-predation’ sites co-occur with large predators that frequently


6


prey on large, adult guppies, while ‘low-predation’ sites only have a single, omnivorous predator that is gape-limited and infrequently preys on smaller guppies (Reznick et al., 1996). Guppies that co-occur with different predators show distinct differences in social, reproductive, and anti-predator behaviors (Houde, 1997; Magurran, 2005). Guppies also express variation in developmental patterns of behavior. For example, guppies from some populations show well developed shoaling behavior from birth through adulthood, others only shoal when they have been startled, while others shoal at birth but, as adults, only shoal when startled (Magurran, 2005; Magurran and Seghers, 1991). Lab studies have shown that the several factors during postbirth development can influence the shoaling behavior in guppies including exposure to predators (Huizinga et al., 2009; Li and Rodd, unpublished data) and interactions with conspecifics (Song et al., 2011). Therefore, guppies provide an exciting range of behavior patterns for study. In contrast, although zebrafish strains do differ in some properties of shoaling, e.g. there are slight between-strain differences in inter-individual distance, strains show similar increases in shoaling behavior over the course of development; that is, increases in shoaling from larva to adult (Mahabir et al., 2013). Furthermore, wild zebrafish populations do not differ in time spent shoaling (Wright et al., 2003). Therefore, guppies could be used to complement studies in zebrafish to develop a comprehensive framework that incorporates several different factors influencing this type of social behavior. This rich array of genetic, ethological and evolutionary information makes the guppy an attractive model for neurological research. A behavior that is frequently studied in neuropsychology and evolutionary biology is risk seeking, or exploratory behavior, defined as the willingness of an individual to investigate novel stimuli (Crusio, 2001). This behavior is of interest to neuropsychologists because of its relation to anxiety, addiction and disease and to evolutionary biologists because of its fitness consequences (e.g. Burns, 2007). Standardized tests, such as the open field test, are widely employed in studies of behavior from insects to mammals to assay exploratory behavior and anxiety. The open field test is simple and highly adaptable and has been used to test a wide range of fish species including guppies (Csanyi and Gerlai, 1988; Gomez-Laplaza and Morgan, 1991; Kleerekoper et al., 1974; Neumeister et al., 2004; Yoshida et al., 2005; specifically guppies: Budaev, 1997; Burns, 2008; Mikheev and Andreev, 1993; Warren and Callaghan, 1975). To determine factors contributing to behavioral differences in the open field test, some studies on lab organisms, including rodents, have recorded behavioral phenotypes of a number of individuals from a given strain and grouped organisms into ‘high’ and ‘low’ responders. Although this approach is useful in providing preliminary associations between behavior and a possible mechanism, it is not clear if these differences are reflective of outbreeding populations, such as humans. For guppies, we know that individuals vary in their degree of exploratory behavior, with individuals originating from populations with a relatively low risk of predation exploring more than individuals originating from populations exposed to more dangerous predators; some, but not all, of this variation has a genetic basis (Burns, 2007). The next steps in this work will be to (1) ask whether levels of neurotransmitters vary across populations, and (2) to manipulate neurotransmitter levels to determine if behavioral phenotypes are altered as would be predicted by studies in other taxa. Preliminary data indicate that, as in rodents (Carrey et al., 2000; Hughes and Greig, 1976), guppies given an acute dose of the pharmaceutical methylphenidate (Ritalin), which affects dopamine levels (Kaplan and Reiss, 1998), increase their exploration of novel objects and environments (De Serrano, Fong and Rodd, unpublished data). This is an excellent example of how methodologies from two very different models can converge. One clear advantage of this guppy system is that the ecological context (predation pressure) has produced, across replicate sets of population, behavioral syndromes; that is, associations between behavioral traits over time, situations or both. For example, guppies experiencing

relatively high predation risk shoal with conspecifics, are less likely to explore novel stimuli and are less aggressive with conspecifics (Burns, 2007; Magurran and Seghers, 1991) than those experiencing low predation risk. Observations of behavioral syndromes are a novel way to ask whether there are common neurophysiological mechanisms underlying integrated sets of behavior and to discover how behaviors are integrated across different scenarios. Using zebrafish as an entry point to these mechanistic studies has already proven advantageous. Norton et al. (2011) report a physiological connection between genetic influences and behavioral syndromes. The authors identified a mutation in the fibroblast growth factor receptor 1a gene (fgf1a) that increased aggression, boldness, and exploratory behavior in zebrafish. The authors demonstrated that Fgf signaling and downstream effects on histamine neurotransmission in the brain mediated the change in behavior. It was also proposed that widespread use of histamine neurotransmission in the brain might serve as a behavioral clustering mechanism in behavioral syndromes (Norton et al., 2011). When strong associations between behaviors are not observed, aspects of the ecological or social environment (e.g., density of conspecifics) can be explored to identify factors involved with the decoupling of these suites of behaviors and will allow us to determine what neurological links have changed. This approach will help to identify stressors that upset normal physiological and behavioral associations. In addition to exploratory behavior, guppies have other well-defined physiological changes and behaviors that could be exploited as markers for neurological disorders. For example, guppies are well known for their mating system; females evaluate males before mating based on male coloration and courtship behavior. Males court females by displaying their multi-colored bodies to females using shimmering motions and typically males spend a huge fraction of their overall time budget pursuing and courting females (who in contrast, spend most of their time foraging) (Magurran and Seghers, 1994). Guppies show considerable variation in the expression and development of courtship behavior. Males increase the number of courtship displays directed at females over the first few weeks post-maturation and the rate of courtship depends on characteristics of their population of origin (high- or lowpredation) and the degree of competition for mates during development. The degree of responsiveness of males to the degree of competition itself varies between populations (Rodd and Sokolowski, 1995). Since healthy males normally spend so much time engaging in these conspicuous behaviors, the absence of these behaviors makes it easy to recognize when males are ill, or otherwise unmotivated to court females. Male guppies also increase the number and area of the black spots on their sides in the presence of females to accentuate their color patterns (Houde, 1997). We propose that reductions in courtship behavior and black spots on male guppies could be a good metric for affective disorders. Consistent with this model, male mice are known to exhibit decreased sexual motivation when they enter depressivelike states; for example, healthy, normal male mice mark territories with urine to attract females and to establish dominance. Males who experience chronic social defeat reduce their scent marking, and the opposite is observed in mice exposed to enriched environments (Lehmann et al., 2013). Chronic administration of a common anti-depressant (fluoxetine) was shown to counteract the endocrine and behavioral effects of social defeat, which further supports the link between decreased libido and depressive-like states in rodents (Lehmann et al., 2013). Therefore, if similar physiological responses can be associated with decreased sexual motivation in male guppies, this will further validate the cross-taxa relevance of this behavior and its link to depression. In addition, the guppy offers other underutilized tools that make them attractive for experimental neuroethological research. For example, guppies possess a patch of chromatophores covering the braincase called the meninx. In response to stress, melanophores aggregate in the meninx, which causes visible darkening in this region (Gibson et al., 2009). This offers a non-invasive way to evaluate the stress response, allowing changes in stress to be monitored over time, e.g.,



during open field tests, and could be coupled with other tests of affective state. 6. Studying the role of maternal environment on brain and behavioral development in guppies and related species Another advantage of studying guppies and related species in the family Poeciliidae is that they are livebearers, carrying their offspring internally for several weeks. This makes them a convenient analog to live bearing in mammalian species. Although embryos carried internally are not as conducive for the study of the development of neuropsychiatric endophenotypes as the transparent embryos of zebrafish, this reproductive mode provides unique opportunities for studies of the effects of maternal environment on neurological development in a non-mammalian model. Within the Poeciliidae family, there is high diversity in reproductive modes, ranging from no placenta (eggs fully provisioned prior to fertilization) to species with intermediate degrees of maternal provisioning to species with full ‘placentation’ (maternal provisioning throughout embryonic development; reviewed in Pollux et al., 2009). Thus, by comparing closely related species that differ in degree of placentation, it will be possible to dissect maternal effects from genetic contributions to neurodevelopmental disorders. This placentation gradient could be utilized to better understand neurological defects caused by environmental teratogens, and also to determine the role of prenatal stress exposure on coping ability later in life (e.g., Shanks and Lightman, 2001). 7. Summary and outlook Although initial research promises a rich future for fish as models for endophenotypes and their genetic, neurobiological, and behavioral consequences, more work needs to be done to fully develop fish as models for answering ongoing questions in neuropsychiatric research. For example, because neuropsychiatric disorders are often classified by symptoms expressed in adulthood, more work is needed to understand the role of neurodevelopmental perturbation on adult behavior. Recent work has added prey capture behavior in zebrafish at later developmental stages (Muto and Kawakami, 2013) and locomotor behavior in adults (Stewart and Kalueff, 2014) to the growing repertoire of zebrafish behavioral assays. We need to define the neurobiological bases of natural behaviors in fish, including sociability, mate search, and territoriality, that may be impacted by neuropsychiatric endophenotypes. Introducing novel model systems such as the guppy, where ecological and behavioral variation is well understood, can help to complement work on organisms that have many genetic tools, but little information on the ecological relevance of observed phenotypes, such as zebrafish. We know a great deal about natural variation in these behaviors in guppies and other species—defining the neurobiological bases for this variation will be hugely informative. We will also be able to perturb development using pharmaceutical and other manipulations and follow the results through adulthood and then ask how successful remediation measures might be used to redirect maladaptive developmental trajectories towards a more typical path. Conversely, more work investigating the neural basis of well-studied behaviors in wild populations of fish is required to maximize transferability of findings between lab and field organisms. We believe that combining the recent shift from modeling bona fide human neuropsychiatric disorders to endophenotypes in animals, along with the incorporation of new animal models and cross-species analysis will benefit neuropsychiatric research in two ways. First, the incorporation of new animal models will provide researchers with a whole suite of animal paradigms in the study of disease, each with a unique set of ecological and practical advantages and constraints. Second, by identifying patterns that are conserved across species, we will move toward a more holistic understanding of the developmental origins and behavioral effects of neurological disorders in humans and other animals.

7

Here, we have shown that fish provide a useful starting point for the development of models to test the neural and behavioral consequences and treatment of neuropsychiatric endophenotypes across species. We believe that this holistic understanding will improve the robustness and transferability of techniques in the identification and treatment of neuropsychiatric disorders. Acknowledgements The authors acknowledge the Natural Sciences and Engineering Research Council (NSERC) of Canada for funding. We also thank the anonymous reviewers for their constructive comments on an earlier version of this manuscript. References Abbott JC, Dunbrack RL, Orr CD. The interaction of size and experience in dominance relationships of juvenile steelhead trout (Salmo gairdneri). Behaviour 1985;92:241–53. Adeyemo OM, Youdim MBH, Markey SP, Markey CJ, Pollard HB. L-Deprenyl confers specific protection against MPTP-induced Parkinson's disease-like movement disorder in the goldfish. Eur J Pharmacol 1993;240:185–93. Barry MJ. Effects of fluoxetine on the swimming and behavioural responses of the Arabian killifish. Ecotoxicology 2012;22:425–32. Batten TFC, Berry PA, Maqbool A, Moons L, Vandesande F. Immunolocalization of catecholamine enzymes, serotonin, dopamine and L-DOPA in the brain of Dicentrarchus labrax (Teleostei). Brain Res Bull 1993;31:233–52. Bearden CE, Freimer NB. Endophenotypes for psychiatric disorders: ready for primetime? Trends Genet 2006;22:306–13. Beaulieu JM, Sotnikova TD, Yao WD, Kockeritz L, Woodgett JR, Gainetdinov RR, et al. Lithium antagonizes dopamine-dependent behaviors mediated by an AKT/glycogen synthase kinase 3 signaling cascade. Proc Natl Acad Sci U S A 2004;101:5099–104. Beaulieu JM, Sotnikova TD, Marion S, Lefkowitz RJ, Gainetdinov RR, Caron MG. An Akt/ β-arrestin 2/PP2A signaling complex mediates dopaminergic neurotransmission and behavior. Cell 2005;122:261–73. Beaulieu JM, Tirotta E, Sotnikova TD, Masri B, Salahpour A, Gainetdinov RR, et al. Regulation of Akt signaling by D2 and D3 dopamine receptors in vivo. J Neurosci 2007;27: 881–5. Bell AM, Backström T, Huntingford FA, Pottinger TG, Winberg S. Variable neuroendocrine responses to ecologically-relevant challenges in sticklebacks. Physiol Behav 2007;91: 15–25. Bell AM, Hankison SJ, Laskowski KL. The repeatability of behaviour: a meta-analysis. Anim Behav 2009;77:771–83. Beltramo M, Krieger M, Tillet Y, Thibault J, Calas A, Mazzi V, et al. Immunolocalization of aromatic L-amino acid decarboxylase in goldfish (Carassius auratus) brain. J Comp Neurol 1994;343:209–27. Berger A. Molecular analysis of the Oryzias latipes (Medaka) transcriptome [Doctoral dissertation] Berlin: Freie Univ; 2010. Bierbach D, Schulte M, Herrmann N, Tobler M, Stadler S, Jung CT, et al. Predator-induced changes of female mating preferences: innate and experiential effects. BMC Evol Biol 2011;11:190. Bisesi JHJ. Impacts of psychotropic pharmaceuticals on hybrid striped bass: altered predation behavior as a function of changes in brain chemistry. Clemson University; 2011 [182 pp.]. Blanchard DC, Sakai RR, McEwen B, Weiss SM, Blanchard RJ. Subordination stress: behavioral, brain, and neuroendocrine correlates. Behav Brain Res 1993;58:113–21. Brown C, Laland K, Krause J. Fish cognition and behavior. second ed. Cambridge, UK: Blackwell Publishing; 2011. Budaev SV. “Personality” in the guppy (Poecilia reticulata): a correlational study of exploratory behavior and social tendency. J Comp Psychol 1997;111:399–411. Burns JG. Intra-specific variation in temperament, spatial memory, and brain size in guppies (Poecilia reticulata) [PhD dissertation] Toronto, Canada: University of Toronto; 2007 [181 pp.]. Burns JG. The validity of three tests of temperament in guppies (Poecilia reticulata). J Comp Psychol 2008;122:344–56. Carrey N, McFadyen MP, Brown RE. Effects of subchronic methylphenidate hydrochloride administration on the locomotor and exploratory behavior of prepubertal mice. J Child Adolesc Psychopharmacol 2000;10:277–86. Castrén E, Elgersma Y, Maffei L, Hagerman R. Treatment of neurodevelopmental disorders in adulthood. J Neurosci 2012;32:14074–9. Clotfelter ED, O'Hare EP, McNitt MM, Carpenter RE, Summers CH. Serotonin decreases aggression via 5-HT1A receptors in the fighting fish Betta splendens. Pharmacol Biochem Behav 2007;87:222–31. Colman JR, Baldwin D, Johnson LL, Scholz NL. Effects of the synthetic estrogen, 17αethinylestradiol, on aggression and courtship behavior in male zebrafish (Danio rerio). Aquat Toxicol 2009;91:346–54. Cozby PC. Methods in behavioral research. 6th ed. Mountain View, CA: Mayfield; 1997. Crandall JE, McCarthy DM, Araki KY, Sims JR, Ren JQ, Bhide PG. Dopamine receptor activation modulates GABA neuron migration from the basal forebrain to the cerebral cortex. J Neurosci 2007;27:3813–22. Crusio WE. Genetic dissection of mouse exploratory behaviour. Behav Brain Res 2001; 125:127–32.


8


Csanyi V, Gerlai R. Open-field behavior and the behavior — genetic analysis of the paradise fish (Macropodus opercularis). J Comp Psychol 1988;102:326–36. Dzieweczynski TL, Hebert OL. Fluoxetine alters behavioral consistency of aggression and courtship in male Siamese fighting fish, Betta splendens. Physiol Behav 2012;107: 92–7. Dunnet SB. Motor function(s) of the nigrostriatal dopamine system: studies of lesions and behavior. In: Dunnet SB, Bentivolglio M, Björklund A, Hökfelt T, editors. Dopamine. Handbook of chemical neuroanatomyNew York: Elsevier; 2005. p. 237–301. Ekstrom P, Honkanen T, Borg B. Development of tyrosine hydroxylase-, dopamine- and dopamine beta-hydroxylase-immunoreactive neurons in a teleost, the three-spined stickleback. J Chem Neuroanat 1992;5:481–501. Fraser BA, Weadick CJ, Janowitz I, Rodd FH, Hughes KA. Sequencing and characterization of the guppy (Poecilia reticulata) transcriptome. BMC Genomics 2011;12:202. Fujimori KE. Characterization of the regulatory region of the dopa decarboxylase gene in medaka: an in vivo green fluorescent protein reporter assay combined with a simple TA-cloning method. Mol Biotechnol 2009;41:224–35. Gaworecki KM, Klaine SJ. Behavioral and biochemical responses of hybrid striped bass during and after fluoxetine exposure. Aquat Toxicol 2008;88:207–13. Gibson R, Burns JG, Rodd FH. Flexibility in the colouration of the meninx (brain covering) in the guppy (Poecilia reticulata): investigations of potential function. Can J Zool 2009;87:529–36. Giorgi O, Deiana AM, Salvadori S, Lecca D, Corda MG. Developmental changes in the content of dopamine in the olfactory bulb of the European eel (Anguilla anguilla). Neurosci Lett 1994;172:35–8. Gomez-Laplaza LM, Morgan E. Effects of short-term isolation on the locomotor activity of the angelfish (Pterophyllum scalare). J Comp Psychol 1991;105:366–75. Gottesman II, Gould TD. The endophenotype concept in psychiatry: etymology and strategic intentions. Am J Psychiatry 2003;260:636–45. Greenwood AK, Wark AR, Fernald RD, Hofmann HA. Expression of arginine vasotocin in distinct preoptic regions is associated with dominant and subordinate behaviour in an African cichlid fish. Proc R Soc B 2008;275:2393–402. Grober MS, George AA, Watkins KK, Carneiro LA, Oliveira RF. Forebrain AVT and courtship in a fish with male alternative reproductive tactics. Brain Res Bull 2002;57:423–5. Henry TB, Black MC. Acute and chronic toxicity of fluoxetine (selective serotonin reuptake inhibitor) in western mosquitofish. Arch Environ Contam Toxicol 2007;54:325–30. Höglund E, Kolm N, Winberg S. Stress-induced changes in brain serotonergic activity, plasma cortisol and aggressive behavior in Arctic charr (Salvelinus alpinus) is counteracted by L-DOPA. Physiol Behav 2001;74:381–9. Holmberg A, Fogel J, Albertsson E, Fick J, Brown JN, Paxéus N, et al. Does waterborne citalopram affect the aggressive and sexual behaviour of rainbow trout and guppy? J Hazard Mater 2011;187:596–9. Homberg JR. Measuring behaviour in rodents: towards translational neuropsychiatric research. Behav Brain Res 2013;236:295–306. Hornby PJ, Piekut DT. Immunoreactive dopamine beta-hydroxylase in neuronal groups in the goldfish brain. Brain Behav Evol 1988;32:252–6. Hornby PJ, Piekut DT. Distribution of catecholamine-synthesizing enzymes in goldfish brains: presumptive dopamine and norepinephrine neuronal organization. Brain Behav Evol 1990;35:49–64. Houde AE. Sex, color, and mate choice in guppies. Princeton University Press; 1997. Howe K, Clark MD, Torroja CF, Torrance J, Berthelot C, Muffato M, et al. The zebrafish reference genome sequence and its relationship to the human genome. Nature 2013; 496:498–503. Hughes RN, Greig AM. Effects of caffeine, methamphetamine and methylphenidate on reactions to novelty and activity in rats. Neuropharmacology 1976;15:673–6. Hurd YL, Hall H. Chapter IX. Human forebrain dopamine systems: characterization of the normal brain and in relation to psychiatric disorders. Handb Chem Neuroanat 2005; 21:525–71. Huizinga M, Ghalambor CK, Reznick DN. The genetic and environmental basis of adaptive differences in shoaling behavior between populations of the Trinidadian guppy. J Evol Biol 2009;22:1860–6. Hyman SE. The diagnosis of mental disorders: the problem of reification. Annu Rev Clin Psychol 2010;6:155–79. Ito H, Yamamoto N. Non-laminar cerebral cortex in teleost fishes? Biol Lett 2009;5: 117–21. Jaffee SR, Price TS. Gene–environment correlations: a review of the evidence and implications for prevention of mental illness. Mol Psychiatry 2007;12:432–42. Jones FC, Grabherr MG, Chan YF, Russell P, Mauceli E, Johnson J, et al. The genomic basis of adaptive evolution in threespine sticklebacks. Nature 2012;484:55–61. Kah O, Dubourg P, Onteniente B, Geffard M, Calas A. The dopaminergic innervation of the goldfish pituitary. Cell Tissue Res 1986;244:577–82. Kaplan DM, Reiss AL. Attention deficit and development disorders. In: Enna SJ, Coyle JT, editors. Pharmacological management of neurological and psychiatric disorders. New York: McGraw-Hill; 1998. [137–176]. Kasahara M, Naruse K, Sasaki S, Nakatani Y, Qu W, Ahsan B, et al. The medaka draft genome and insights into vertebrate genome evolution. Nature 2007;447:714–9. Kleerekoper H, Matis J, Gensler P, Maynard P. Exploratory behaviour of goldfish Carassius auratus. Anim Behav 1974;22:124–32. Krab LC, de Goede-Bolder A, Aarsen FK, Pluijm SM, Bouman MJ, van der Geest JN, et al. Effect of simvastatin on cognitive functioning in children with neurofibromatosis type 1: a randomized controlled trial. JAMA 2008;300:287–94. Krubitzer L, Campi KL, Cooke DF. All rodents are not the same: a modern synthesis of cortical organization. Brain Behav Evol 2011;78:51–93. Kuz'mina VV, Garina DV. The effects of peripherally injected serotonin on feeding and locomotor activities in carp Cyprinus carpio L. Inland Water Biol 2013;6:62–9. Larson ET, O'Malley DM, Melloni Jr RH. Aggression and vasotocin are associated with dominant–subordinate relationships in zebrafish. Behav Brain Res 2006;167:94–102.

Leal E, Fernández-Durán B, Agulleiro MJ, Conde-Siera M, Míguez JM, Cerdá-Reverter JM. Effects of dopaminergic system activation on feeding behavior and growth performance of the sea bass (Dicentrarchus labrax): a self-feeding approach. Horm Behav 2013;64:113–21. Leder EH, Merilä J, Primmer CR. A flexible whole-genome microarray for transcriptomics in three-spine stickleback (Gasterosteus aculeatus). BMC Genomics 2009;10:426. Lee BY, Howe AE, Conte MA, D'Cotta H, Pepey E, Baroiller JF, et al. An EST resource for tilapia based on 17 normalized libraries and assembly of 116,899 sequence tags. BMC Genomics 2010;11:278. Lehmann ML, Geddes CE, Lee JL, Herkenham M. Urine scent marking (USM): a novel test for depressive-like behavior and a predictor of stress resiliency in mice. PLoS One 2013;8(7):e69822. Lorenzi V, Carpenter RE, Summers CH, Earley RL, Grober MS. Serotonin, social status and sex change in the bluebanded goby Lythrypnus dalli. Physiol Behav 2009;97:476–83. Lorenzi V, Mehinto AC, Denslow ND, Schlenk D. Effects of exposure to the beta-blocker propranolol on the reproductive behavior and gene expression of the fathead minnow, Pimephales promelas. Aquat Toxicol 2012;116–117:8–15. Magurran AE. Evolutionary ecology: the Trinidadian guppy. Oxford University Press; 2005. Magurran AE, Seghers BH. Variation in schooling and aggression amongst guppy (Poecilia reticulata) populations in Trinidad. Behaviour 1991;118:214–34. Magurran AE, Seghers HE. A cost of sexual harassment in the guppy, Poecilia reticulata. Proc R Soc Lond B 1994;258:89–92. Mahabir S, Chatterjee D, Buske C, Gerlai R. Maturation of shoaling in two zebrafish strains: a behavioral and neurochemical analysis. Behav Brain Res 2013;247:1–8. Marsh KE, Creutz LM, Hawkins MB, Godwin J. Aromatase immunoreactivity in the bluehead wrasse brain, Thalassoma bifasciatum: immunolocalization and co-regionalization with arginine vasotocin and tyrosine hydroxylase. Brain Res 2006;1126:91–101. Matsui H, Taniguchi Y, Inoue H, Uemura K, Takeda S, Takahashi R. A chemical neurotoxin, MPTP induces Parkinson's disease like phenotype, movement disorders and persistent loss of dopamine neurons in medaka fish. Neurosci Res 2009;65:263–71. Matsui H, Gavinio R, Asano T, Uemura N, Ito H, Taniguchi Y, et al. PINK1 and Parkin complementarily protect dopaminergic neurons in vertebrates. Hum Mol Genet 2013;22: 2423–34. McGrath PT, Rockman MV, Zimmer M, Jang H, Macosko EZ, Kruglyak L, et al. Quantitative mapping of a digenic behavioral trait implicates globin variation in C. elegans sensory behaviors. Neuron 2009;61:692–9. McLean DL, Fetcho JR. Ontogeny and innervation patterns of dopaminergic, noradrenergic, and serotonergic neurons in larval zebrafish. J Comp Neurol 2004;480:38–56. Mikheev VN, Andreev OA. Two-phase exploration of a novel environment in the guppy, Poecilia reticulata. J Fish Biol 1993;42:375–83. Money KM, Stanwood GD. Developmental origins of brain disorders: role for dopamine. Front Cell Neurosci 2013;7:260. Munro AD. Effects of melatonin, serotonin, and naloxone on aggression in isolated cichlid fish (Aequidens pulcher). J Pineal Res 1986;3:257–62. Muto A, Kawakami K. Prey capture in zebrafish larvae serves as a model to study cognitive functions. Front Neural Circuits 2013;7. Neumeister H, Cellucci CJ, Rapp PE, Korn H, Faber DS. Dynamical analysis reveals individuality of locomotion in gold-fish. J Exp Biol 2004;207:697–708. Norton WHJ, Stumpenhorst K, Faus-Kessler T, Folchert A, Rohner N, Harris MP, et al. Modulation of fgfr1a signaling in zebrafish reveals a genetic basis for the aggression– boldness syndrome. J Neurosci 2011;31:13796–807. O'Connell LA, Hofmann HA. The vertebrate mesolimbic reward system and social behavior network: a comparative synthesis. J Comp Neurol 2011;519(18):3599–639. O'Connell LA, Fontenot MR, Hofmann HA. Characterization of the dopaminergic system in the brain of an African cichlid fish, Astatotilapia burtoni. J Comp Neurol 2011;519: 75–92. O'Connell LA, Hofmann HA. Evolution of a vertebrate social decision-making network. Science 2012;336:1154–7. O'Connell LA, Fontenot MR, Hofmann HA. Neurochemical profiling of dopaminergic neurons in the forebrain of a cichlid fish, Astatotilapia burtoni. J Chem Neuroanat 2013;47:106–15. O'Kane CJ. Drosophila as a model organism for the study of neuropsychiatric disorders. In: Hagan JJ, editor. Molecular and functional models in neuropsychiatry. Berlin: Springer; 2011. p. 37–60. Oldfield RG, Hofmann HA. Neuropeptide regulation of social behavior in a monogamous cichlid fish. Physiol Behav 2011;102:296–303. Øverli Ø, Harris AH, Winberg S. Short-term effects of fights for social dominance and the establishment of dominant–subordinate relationships on brain monoamines and cortisol in rainbow trout. Brain Behav Evol 1999;54:263–75. Panula P, Sallinen V, Sundvik M, Kolehmainen J, Torkko V, Tiittula A, et al. Modulatory neurotransmitter systems and behavior: towards zebrafish models of neurodegenerative diseases. Zebrafish 2006;3:235–47. Parafati M, Senatori O, Nicotra A. Localization of tyrosine hydroxylase immunoreactive neurons in the forebrain of the guppy Poecilia reticulata. J Fish Biol 2009;75: 1194–205. Parker MO, Brennan CH. Zebrafish (Danio rerio) models of substance abuse: harnessing the capabilities. Behaviour 2012;149:10–2. Peng J, Wagle M, Mueller T, Mathur P, Lockwood BL, Bretaud S, et al. Ethanol-modulated camouflage response screen in zebrafish uncovers a novel role for cAMP and extracellular signal-regulated kinase signaling in behavioral sensitivity to ethanol. J Neurosci 2009;29:8408–18. Perreault H, Semsar K, Godwin J. Fluoxetine treatment decreases territorial aggression in a coral reef fish. Physiol Behav 2003;79:719–24. Petzold AM, Balciunas D, Sivasubbu S, Clark KJ, Bedell VM, Westcot SE, et al. Nicotine response genetics in the zebrafish. Proc Natl Acad Sci U S A 2009;106:18662–7.


Z.J. Hall et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry xxx (2014) xxx–xxx Pickart MA, Klee EW. Zebrafish approaches enhance the translational research tackle box. Transl Res 2014;163:65–8. Pollux BJA, Pires MN, Banet AI, Reznick DN. Evolution of placentas in the fish family Poeciliidae: an empirical study of macroevolution. Annu Rev Ecol Evol Syst 2009; 40:271–89. Portugues R, Engert F. The neural basis of visual behaviors in the larval zebrafish. Curr Opin Neurobiol 2009;19:644–7. Raghuveer CC, Sudhakumari B, Senthilkumaran B, Kagawa H, Dutta-Gupta A, Nagahama Y. Gender differences in tryptophan hydroxylase-2 mRNA, serotonin, and 5hydroxytryptophan levels in the brain of catfish, Clarias gariepinus, during sex differentiation. Gen Comp Endocrinol 2011;171:94–104. Reus VI, Freimer NB. Understanding the genetic basis of mood disorders: where do we stand? Am J Hum Genet 1997;60:1283–8. Reznick DN, Butler IV MJ, Rodd FH, Ross P. Life history evolution in guppies (Poecilia reticulata). 6. Differential mortality as a mechanism for natural selection. Evolution 1996;50:1651–60. Reznick DN, Bryant M, Roff DA, Ghalambor G, Ghalambor DE. Effects of extrinsic mortality on the evolution of senescence in guppies. Nature 2004;431:1095–9. Reznick D, Bryant M, Holmes D. The evolution of senescence and post-reproductive lifespan in guppies (Poecilia reticulata). PLoS Biol 2006;4:136–43. Robinson TE, Berridge KC. The incentive sensitization theory of addiction: some current issues. Philos. Trans. R. Soc. Lond. B Biol. Sci. 2008;363:3137–46. Rodd FH, Sokolowski MB. Complex origins of variation in the sexual behaviour of male Trinidadian guppies, Poecilia reticulata: interactions between social environment, heredity, body size and age. Anim Behav 1995;49:1139–59. Schultz MM, Painter MM, Bartell SE, Logue A, Furlong ET, Werner SL, et al. Selective uptake and biological consequences of environmentally relevant antidepressant pharmaceutical exposures on male fathead minnows. Aquat Toxicol 2011;104:38–47. Schweitzer J, Driever W. Development of the dopamine systems in zebrafish. In: Pasterkamp RJ, Smidt MP, Burbach JPH, editors. Development and engineering of dopamine neurons. New York: Springer; 2009. p. 1–14. Shamchuk AL, Tierney KB. Phenotyping stimulus evoked responses in larval zebrafish. Behaviour 2012;149:1177–203. Shanks N, Lightman SL. The maternal–neonatal neuro-immune interface: are there longterm implications for inflammatory or stress-related disease? J Clin Invest 2001;108: 1567–73. Smulders TV. The relevance of brain evolution for the biomedical sciences. Biol Lett 2009; 5:138–40. Song Z, Boenke MC, Rodd FH. Interpopulation differences in shoaling behaviour in guppies (Poecilia reticulata): roles of social environment and population origin. Ethology 2011; 117:1009–18. Souza BR, Romano-Silva MA, Tropepe V. Dopamine D2 receptor activity modulates Akt signaling and alters GABAergic neuron development and motor behavior in zebrafish larvae. J Neurosci 2011;31:5512–25. Souza BR, Tropepe V. The role of dopaminergic signalling during larval zebrafish brain development: a tool for investigating the developmental basis of neuropsychiatric disorders. Rev Neurosci 2011;22:107–19. Stewart AM, Kalueff AV. Developing better and more valid animal models of brain disorders. Behav Brain Res 2014. http://dx.doi.org/10.1016/j.bbr.2013.12.024. [in press]. Stewart AM, Kalueff AV. The behavioral effects of acute Δ9-tetrahydrocannabinol and heroin (diacetylmorphine) exposure in adult zebrafish. Brain Res 2014b;1543:109–19. Strausfeld NJ, Hirth F. Deep homology of arthropod central complex and vertebrate basal ganglia. Science 2013;340:157–61.

9

Takesian AE, Hensch TK. Balancing plasticity/stability across brain development. Prog Brain Res 2013;207:3–34. Tiersch TR, Griffith JS. Apomorphine-induced vomiting in rainbow trout (Salmo gairdneri). Comp Biochem Physiol A 1988;91:721–5. Trainor BC, Hofmann HA. Somatostatin regulates aggressive behavior in an African cichlid fish. Endocrinology 2006;147:5119–25. Tropepe V, Sive HL. Can zebrafish be used as a model to study the neurodevelopmental causes of autism? Genes Brain Behav 2003;2:268–81. Vacher C, Pellegrini E, Anglade I, Ferriére FO, Saligaut C, Kah O. Distribution of dopamine D2 receptor mRNAs in the brain and the pituitary of female rainbow trout: an in situ hybridization study. J Comp Neurol 2003;458:32–45. Valenti Jr TW, Gould GG, Berninger JP, Connors KA, Keele NB, Prosser KN, et al. Human therapeutic plasma levels of the selective serotonin reuptake inhibitor (SSRI) sertraline decrease serotonin reuptake transporter binding and shelter-seeking behavior in adult male fathead minnows. Environ Sci Technol 2012;46:2427–35. Vesterlund L, Jiao H, Unneberg P, Hovatta O, Kere J. The zebrafish transcriptome during early development. BMC Dev Biol 2011;11:30. Vetillard A, Benanni S, Saligaut C, Jego P, Balihache T. Localization of tyrosine hydroxylase and its messenger RNA in the brain of rainbow trout by immunocytochemistry and in situ hybridization. J Comp Neurol 2002;449:374–89. Volkoff H. The effects of amphetamine injections on feeding behavior and the brain expression of orexin, CART, tyrosine hydroxylase (TH) and thyrotropin releasing hormone (TRH) in goldfish (Carassius auratus). Fish Physiol Biochem 2013;39: 979–91. Warren EW, Callaghan S. Individual differences in response to an open-field test by guppy Poecilia reticulata (Peters). J Fish Biol 1975;7:105–13. Williams GV, Castner SA. Under the curve: critical issues for elucidating D1 receptor function in working memory. Neuroscience 2006;139:263–76. Winberg S, Nilsson GE. Induction of social dominance by L-DOPA treatment in Arctic charr. Neuroreport 1992;3:243–6. Winberg S, Nilsson GE. Roles of brain monoamine neurotransmitters in agonistic behaviour and stress reactions, with particular reference to fish. Comp Biochem Physiol C 1993;106:597–614. Winberg S, Nilsson GE. Multiple high-affinity binding sites for [3H] serotonin in the brain of a teleost fish, the arctic charr (Salvelinus alpinus). J Exp Biol 1996;199:2429–35. Winberg S, Winberg Y, Fernald RD. Effect of social rank on brain monoaminergic activity in a cichlid fish. Brain Behav Evol 1997;49:230–6. Winberg S, Lepage O. Elevation of brain 5-HT activity, POMC expression, and plasma cortisol in socially subordinate rainbow trout. Am J Physiol 1998;274: R645–54. Winder VL, Pennington PL, Hurd MW, Wirth EF. Fluoxetine effects on sheepshead minnow (Cyprinodon variegatus) locomotor activity. J Environ Sci Health B 2012;47:51–8. Wöhr M, Scattoni ML. Behavioural methods used in rodent models of autism spectrum disorders: current standards and new developments. Behav Brain Res 2013;251: 5–17. Wright D, Rimmer LB, Pritchard VL, Krause J, Butlin RK. Inter and intra-population variation in shoaling and boldness in the zebrafish (Danio rerio). Naturwissenschaften 2003;90:374–7. Yoshida M, Nagamine M, Uematsu K. Comparison of behavioral responses to a novel environment between three teleosts, bluegill Lepomis macrochirus, crucian carp Carassius langsdorfii, and goldfish Carassius auratus. Fish Sci 2005;71:314–9.
