may be involved in the transport of PRL from blood to cerebros- ..... and frozen in powdered dry ice. .... Foster RG, Plowman G, Goldsmith AR, Follett BK. (1987). Immuno- histochemical demonstration of marked changes in the LHRH system.
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Journal of Neuroendocrinology, Vol. 2, NO. 5
Changes in Feeding Activity, Plasma Luteinizing Hormone, and Testes Weight in Ring Doves FoIlowing Hypothalamic Injections of Pro1act in Kenneth T. Foreman?', Robert W. Leaf and J o h n
p. B u n t i n t
+ Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201, USA $ School of Applied Biology, Lancashire Polytechnic, Preston Pi31 2TQ, UK. Key words: prolactin, ventromedial hypothalamus, preoptic area, feeding, luteinizing hormone.
Abstract Microinjections of ovine prolactin were administered unilaterally to the ventromedial hypothalamic nucleus and the preopticsuprachiasmatic region in adult male ring doves in an attempt to determine the site(s) at which intracranial injections of prolactin act to alter feeding behaviour and gonadotropin secretion in this species. Food intake and body weight were measured daily during a 6day pretreatment period and the 5-day treatment period that immediately followed. During the treatment period, birds received twice daily injections (0.5 PI) of either 2.5 ng ovine prolactin or saline vehicle. An additional group of birds with cannulae in the ventromedial nucleus were given twice daily injections of 25 ng ovine prolactin. Although food consumption was unaffected by low dose prolactin treatment, birds given 25 ng prolactin injections into the ventromedial nucleus showed a significant augmentation i n food intake. Injections of 25 ng prolactin into the preoptic area also increased feeding; however, the magnitude of this hyperphagic response, as expressed relative to pretreatment levels, was less than that observed following prolactin injection into the ventromedial nucleus. No differences were observed between prolactin-treated and vehicle-treated birds in either cannulation group when testes weights and plasma luteinizing hormone concentrations were compared at the end of the treatment period. However, the possibility that prolactin influenced changes in luteinizing hormone and testes weight relative to baseline values could not be assessed due to constraints imposed by the experimental paradigm used. These results suggest that prolactin-sensitive neurons in the ventromedial hypothalamic region and the preoptic area are potential sites of prolactin action in promoting hyperphagia in ring doves. However, the role of these sites in mediating prolactin-induced suppression of gonadotropin secretion in this species remains to be clarified.
In addition to its remarkably diverse physiological actions in vertebrates (I), prolactin (PRL) also influences a wide variety of behaviour patterns, including changes in sexual activity (2-4), parental responsiveness (5-7), feeding (&lo), grooming (1 1, 12) and yawning (13). Although the sites of PRL action in promoting these behavioural changes remain largely unexplored, neurophysiological and neurochemical evidence suggests that PRL is capable of influencing brain activity directly (14-16). This view is strengthened by evidence for PRL binding sites in specific forebrain regions of the rabbit (17), pig (18), horse (19), toad (20) and ring dove (21, 22). PRL binding has also been reported in the choroid plexus of rat (23), horse, calf (19), ring dove (24), sheep, pig and rabbit (18). Although their function has yet to be established, it has been proposed that PRL binding sites in the choroid plexus may be involved in the transport of PRL from blood to cerebros-
pinal fluid (25), thereby providing a possible route by which blood-borne PRL could gain access to target cells in periventricular brain areas. It is also conceivable that behaviour is influenced by PRL-like molecules of CNS origin that have been detected in the brains of mammalian (26-28) and non-mammalian species (29, 30). Although changes in behaviour and reproductive condition have been demonstrated in several vertebrate species following intracranial administration of PRL, these alterations have been particularly well documented in ring doves (Streptopelia risoria). Intracerebroventricular (icv) injections of PRL dramatically increase food intake in ring doves (31, 32), with males showing a greater response than females. Intracerebroventricular injections of PRL have also been shown to reduce plasma luteinizing hormone (LH) levels (33) and to cause gonadal regression in this
'Present address: St. Louis University School of Medicine, 1402 South Grand Boulevard, St. Louis, Missouri 63104, USA. Correspondence 10; J. D. Buntin, Department of Biological Sciences, P.O. Box 413, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 5321 1,
USA.
668 Brain sites of PRL action species (31, 33). While the sites at which PRL acts to alter behaviour and reproductive conditions have yet to be established, the distribution of PRL binding sites has recently been determined in the ring dove brain using quantitative autoradiography (22). Although specific binding of [‘Z’I]ovine (0)PRL was detected in several brain regions, areas of concentrated binding activity were restricted to the preoptic area (POA) and several discrete regions of the dove hypothalamus, including the suprachiasmatic nucleus, paraventricular nucleus (PVN), ventromedial nucleus (VMN), choroid plexus and tuberoinfundibular region. In the current study, microinjection procedures were employed to examine the role of two PRL-sensitive brain regions, the VMN and the POA/suprachiasmatic region, as possible sites of PRL action in mediating the marked increase in food intake and the gonadotropin suppression that have been previously reported in ring doves following icv injections of the hormone. These sites were selected for analysis based on extensive evidence from lesion studies and neurochemical studies for VMN involvement in food intake regulation in birds (34, 35) and for gonadotropin-releasing hormone (GnRH)-containing cell bodies in the avian POA that are presumed to regulate pituitary gonadotropin secretion (36-39).
Results A 0.2 to 0.3 mm area of tissue damage was typically found at the site of the injection cannula tip when brains were examined for verification of proper cannula placement. This region was part of a larger (0.8 to 1.O mm) teardrop-shaped or cylinder-shaped region of dye infiltration that surrounded the base and sides of the injection cannula tract. The location of cannula tips for doves treated with twice daily injections of 25 ng oPRL in Experiments 1 and 2 were defined by reference to (40) and (41) and are shown in Fig. 1. Two of the birds represented in this figure (coronal section A6.75) were excluded from the analysis because the cannula tips did not encompass the target area. A third bird (coronal section A5.25) was excluded because its ink distribution encompassed both the VMN and a portion of the PRL-sensitive tuberal region. All remaining birds had cannula tips that either penetrated the VMN or POA or contacted the lateral borders of these regions. In addition to the PRL-treated birds depicted in Fig. I , 17 other doves receiving PRL or vehicle were discarded from Experiments 1 and 2 because of improper cannula placement or because dye administration at the end of the experiment revealed leakage of injected material into the cerebral ventricles. One 25 ng oPRLtreated bird in the VMN group was also excluded because its plasma LH concentration was found to be over three times higher than the next highest value in the same treatment condition, thus identifying it as a significant outlier (Q test: P
