Dopamine involvement in the regulation of ...

Dopamine involvement in the regulation of gonadotropin secretion in coho salmon GLENVANDERKRAAK' Department of Zoology, University of British Columbia, Vancouver, B . C . , Canada V6T 1W5

EDWARD M. DONALDSON Department of Fisheries and Oceans, Fisheries Research Branch, 4160 Marine Drive, West Vancouver, B.C., Canada V7V IN6 AND

Can. J. Zool. Downloaded from www.nrcresearchpress.com by Depository Services Program on 05/28/13 For personal use only.

JOHNP. CHANG Department of Zoology, University of Alberta, Edmonton, Alta., Canada T6G 2E9 Received October 29. 1985

and J. P. CHANG.1986. Dopamine involvement in the regulation of gonadotropin VANDERKRAAK,G., E. M. DONALDSON, secretion in coho salmon. Can. J . Zool . 64: 1245- 1248. hormone-releasing hormone (LHRH-A) The effects of intraperitoneal injections of [D-~la~,~ro~-N-ethylamidel-luteinizing and pimozide, a dopamine receptor antagonist, on plasma gonadotropin levels and ovulation in coho salmon were investigated. Both LHRH-A (0.02 mg/kg body weight) and pimozide (10 mg/kg body weight) stimulate gonadotropin secretion, with LHRH-A causing a more rapid onset of gonadotropin release and a higher magnitude increase in plasma gonadotropin levels than pimozide. Pimozide caused a marked potentiation of the gonadotropin release response to LHRH-A. Injections of LHRH-A alone and in combination with pimozide were effective means of inducing ovulation, whereas pimozide alone was ineffective. These data support the concept that dopamine participates in the regulation of gonadotropin secretion in teleosts and suggest that doparnine has a minor role in the regulation of ovulatory gonadotropin changes in coho salmon compared with cyprinids. VAN DER KRAAK,G., E. M. DONALDSON et J. P. CHANG.1986. Dopamine involvement in the regulation of gonadotropin secretion in coho salmon. Can. J. Zool. 64: 1245- 1248. On trouvera ici les rksultats d'une Ctude sur les effets d'injections intra-abdominales d'un antagoniste de I'hormone de IibCration de la IutCo-stimuline, le [ ~ - ~ l a ~ , ~ r o ~ - ~ - C t h y l a(LHRH-A), m i d e ] - ~et~ d'un ~ ~ antogoniste des rkcepteurs de la dopamine, le pimozide, sur les concentrations de gonadotropine plasmatique et sur l'ovulation de saumons coho. Les deux produits (LHRH-A a raison de 0,02 mg/kg, et pimozine a raison de 10 mg/kg) stimulent la sCcrCtion de gonadotropine, mais le LHRH-A dCclenche plus rapidement la IibCration de la gonadotropine et entraine une augmentation plus considkrable des concentrations de gonadotropine dans le plasma. Le pimozide accentue le processus de libkration de a gonadotropine en rCaction au LHRH-A. Des injections de LHRH-A seul ou combink au pimozide constituent un moyen efficace de declencher I'ovulation, alors que les injections de pimozide seul restent inefficaces. Ces rCsultats corroborent I'hypothitse selon laquelle la dopamine participe au contrale de la sCcrCtion de gonadotropine chez les tClCostCens et permettent de croire que la dopamine ne joue qu'un rale secondaire dans la rkgulation des variations de la gonadotropine ovulatoire chez le saumon coho, contrairement a la situation qui prCvaut chez les cyprinidCs. [Traduit par la revue]

Introduction Recent studies have demonstrated dual neuroendocrine control of gonadotropin secretion in goldfish (Carassius auratus), with gonadotropin release stimulated by gonadotropin-releasing hormone (GnRH) and inhibited by a gonadotropin release inhibitory factor (GRIF) (see Peter 1983a , 1983b) . Further studies suggest that dopamine functions as a GRIF in goldfish by blocking spontaneous release of gonadotropin and modulating the action of GnRH (Chang and Peter 1983a; Chang et al. 1983, 1984). Based on the actions of the dopamine antagonist pimozide on basal as well as GnRH-stimulated gonadotropin release and (or) ovulation, dopamine appears to play a role in controlling gonadotropin release in several teleost species in addition to goldfish (Chang and Peter 1983b; Sokolowska et al. 1984), including the African catfish Clarius larzera (de Leeuw et al. 1985), European eel Anguilla anguilla (Dufour et al. 1984), loach Paramisgurnus dabyranus (Lin et al. 1985), and several carp species (Billard et al. 1983; Lin et al. 1986). While several studies have demonstrated that GnRH is highly effective in stimulating gonadotropin release in salmonids (e.g . , Crim et al. 1983; Van Der Kraak et al. 1983, 1985), only limited data are available with respect to the involvement of dopamine in the regulation of gonadotropin secretion. Crim ( 1981) reported that dopamine inhibited the release of gonadotropin from rain' ~ d d r e s for s correspondence: Department of Zoology, University of Alberta, Edmonton, Alta., Canada T6G 2E9.

bow trout (Salmo gairdneri) pituitaries incubated in vitro, and recently Billard et al. (1984) reported that pimozide increased circulating gonadotropin levels in rainbow trout. In the present study, we have investigated the effects of pimozide and [D-~ 1 a ~ ; P rN-N-ethylamidel o~-1uteinizing hormone-releas ing hormone (LHRH-A) on plasma gonadotropin levels and ovulation in adult coho salmon (Oncorhynchus kisutch).

Materials and methods Adult female coho salmon were obtained from the Capilano Salmon Hatchery following their anadromous migration. Fish were transferred to the West Vancouver Laboratory, Fisheries and Oceans, and held outdoors in 3 m diameter fiberglass tanks supplied with freshwater at 10°C. The fish were held for 1 week prior to treatment and screened immediately before injection to exclude fish with oocytes that had undergone germinal vesicle breakdown. The procedures for anesthetization, weighing, and tagging of fish are detailed in Hunter et al. (1978) and Van Der Kraak et al. (1983). LHRH-A and pimozide were donated by Syndel Laboratories, Vancouver, B.C., and Janseen Pharmaceuticals Ltd., Beerse, Belgium, respectively. LHRH-A was dissolved in 0.65% saline whereas pimozide was suspended in saline containing 0.1% sodium metabisulphite. Four groups of 8 or 9 fish were given injections of either saline, LHRH-A (0.02 mg/kg), pimozide (10 mg/kg), or a combination of pimozide and LHRH-A. Test compounds were injected intraperitoneally at the base of the pelvic fin with injection volumes adjusted to 0.4 mL/kg body weight. Blood samples were obtained at the time of injection and 1.5, 6, 24, 48, and 96 h postinjection by puncturing the

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CAN. J. ZOOL. VOL. 64, 1986

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TABLE1. The effects of pimozide and LHRH-A on ovulation in coho salmon. Values reported are the cumulative number of fish that had ovulated by days 4, 6, and 8 for all treated fish and after screening to eliminate fish of advanced sexual maturity at the time of injection

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Total no. ovulated by:

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(9)

HOUR FIG. 1. Effects of pimozide and LHRH-A on plasma gonadotropin levels (mean ? SE) in coho salmon. At each sampling period, plasma gonadotropin levels that are similar (P < 0.05) as determined by Duncan's multiple range test are identified by the same letter. caudal vasculature with a 21-gauge needle attached to a 2.5-mL syringe. Plasma was obtained following centrifugation and stored at -40°C prior to gonadotropin determination by radioimmunoassay (Van Der Kraak et al. 1983). In addition, 17a,20P-dihydroxy-4-pregnen3-one (17a20PP) levels in the preinjection blood samples were determined by radioimmunoassay (Van Der Kraak et al. 1984). Fish were checked for ovulation on days 4, 6 , and 8. Gonadotropin data were analysed by one-way analysis of variance and Duncan's multiple range test following loglotransformation. The Mann-Whitney U-test was used to compare the rate of ovulation between experimental and control groups.

Results Plasma gonadotropin levels were increased following single intraperitoneal injections of either pimozide or LHRH-A (Fig. 1). Pimozide had a delayed action, resulting in higher plasma gonadotropin levels at 48 and 96 h postinjection when compared with saline-injected fish. In contrast, injection of LHRH-A increased plasma gonadotropin levels within 1.5 h and maintained elevated gonadotropin levels for up to 48 h when compared with pimozide-injected fish; gonadotropin levels were similar in pimozide-injected and LHRH-A injected fish at 96 h. Fish receiving a combined injection of pimozide and LHRH-A had higher plasma gonadotropin levels than LHRH-A injected fish from 6 to 96 h postinjection. In the pimozide-injected group, 3 out of 9 fish had ovulated by day 4 compared with 1 out of 8 or 9 fish in the other treatment groups (Table 1, A). By day 8 , only one additional fish had ovulated in the pimozide and saline-injected groups. In contrast, 7 out of 8 fish receiving LHRH-A and 8 out of 9 fish receiving pimozide and LHRH-A had ovulated by day 8 . The marked asynchrony in the time of ovulation, particularly in the pimozide-injected group, suggests that in some fish, ovulation may not have been due to the treatment but had occurred spontaneously as a result of advanced sexual maturity. To investigate this possibility, 17ar20PP levels in preinjection blood samples were determined as previous studies have shown that plasma levels of this hormone are elevated several days prior to spontaneous ovulation (Van Der Kraak et ul. 1984, 1985). Several fish utilized in this study had elevated 17ar20PP levels, which was consistent with an advanced stage of sexual

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day 4

day 6

day 8

Saline Pimozide LHRH-A Pimozide and LHRH-A

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(B) After screening Saline Pimozide LHRH-A Pimozide and LHRH-A

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(A) All treated fish

"Includes one non-ovulated fish dead on day 6. *Significantly greater than saline injected group ( P < 0.05). **Significantly greater than saline injected and p i m o ~ i d einjected groups ( P < 0.05)

maturity (data not shown). Accordingly, those fish with elevated 17ar20PP levels were eliminated from consideration when determining treatment effects on ovulation. As a result, injection of both LHRH-A alone and in combination with pimozide were found to be more effective in inducing ovulation than saline or pimozide injections (Table 1, B). The presence of fish of advanced sexual maturity in each of the treatment groups did not alter the interpretation of treatment effects on plasma gonadotropin levels.

Discussion Consistent with previous studies (Van Der Kraak et ul. 1983, 1985), administration of LHRH-A resulted in a prolonged increase in plasma gonadotropin levels in preovulatory coho salmon (Fig. 1). The present results also demonstrate that pimozide, although less effective than LHRH-A, also stimulates an increase in plasma gonadotropin levels and causes a marked potentiation of the action of LHRH-A. These findings support the concept of dual neuroendocrine mechanisms regulating gonadotropin secretion in teleosts with dopamine acting as a GRIF. In coho salmon, pimozide alone did not influence plasma gonadotropin levels for 24 h but caused a marked potentiation of the gonadotropin release response to LHRH-A by 6 h (Fig. 1). Studies on goldfish have shown that treatment with pimozide alone has a variable influence on serum gonadotropin levels with the response influenced by both temperature and the reproductive condition of the fish (Chang and Peter 19836; Sokolowska c't ul. 1984; Sokolowska, Peter, and Nahorniak 1985; Sokolowska, Peter, Nahorniak, and Chang 1985). As in the present study, pimozide has a delayed action on goldfish acclimated to 12"C, stimulating an increase in serum gonadotropin levels in 24 to 48 h (Sokolowska, Peter, and Nahorniak 1985). However, studies on goldfish held at 12°C have shown that pretreatment with pimozide is necessary to demonstrate potentiation of the gonadotropin release response to LHRH-A. For example in goldfish held at 12"C, pimozide injected with the first or second of two LHRH-A injections given 12 h apart or prior to a single injection of LHRH-A potentiate the gonadotropin release response to LHRH-A; simultaneous injections of pimozide and LHRH-A were no more effective than LHRH-A

VAN DER KRAAK ET AL.

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CHANG,J. P., A. F. COOK,and R. E. PETER.1983. Influence of catecholamines on gonadotropin secretion in goldfish Carassius auratus. Gen. Comp. Endocrinol. 49: 22-3 1. CHANG, 'J. P., and R. E. PETER.1983a. Effects of dopamine on gonadotropin release in female goldfish, Carassius auratus. Neuroendocrinology. 36: 35 1-357. 1983b. Effects of pimozide and d e s - ~ l ~ ~ O [ luteinizing ~-~la~] hormone releasing hormone ethylamide on serum gonadotropin concentrations, germinal vesicle migration and ovulation in female goldfish, Carassius auratus. Gen. Comp. Endocrinol. 52: 30-37. CHANG, J. P., R. E. PETER,C. S. NAHORNIAK, and M. SOKOI,OWSKA. 1984. Effects of catecholaminergic agonists and antagonists on serum gonadotropin concentrations and ovulation in goldfish: Evidence for specificity of dopamine inhibition of gonadotropin secretion. Gen. Comp. Endocrinol. 55: 35 1-360. CRIM,L. W. 1981. Control of gonadotropic hormone secretion (GtH) by the rainbow trout pituitary gland: evidence of GtH inhibition by catecholamine and stimulation of GtH release by some other neuroregulatory factors. In Neurosecretion. Edited by K. Lederis and D. S. Farner. Plenum Publishing Corp., New York. p. 246. CRIM,L. W., D. M. EVANS, and B. H. VICKERY. 1983. Manipulation of the seasonal reproductive cycle of the landlocked salmon (Salmo salar) with LH-RH administration at various stages of gonadal development. Can. J. Fish Aquat. Sci. 40: 61-67. DE LEEUW, R., J. W. RESINK, E. J. M. ROOYAKKERS, and H. J. TH. Goos. 1985. Pimozide modulates the luteinizing hormone-releasing hormone effect on gonadotropin release in the African catfish, Clarius lazera. Gen . Comp. Endocrinol . 58: 120- 127. DUFOUR,S., N. DELERUE-LE BELLE,and Y. A. FONTAINE. 1984. Stimulation de la liberation d'hormone gonadotrope et du developpment des gonades sous l'effet conjuge du pimozide et d'un agoniste de la LHRH chez l'anguille femelle argentee pretraitee a l'oestradiol. C. R. Hebd. Seances Acad. Sci. Ser. 3, 299: 231-234. FOSTIER, A., and B. JALABERT. 1982. Physiological basis of practical means to induce ovulation in fish. In Proceedings of the International Symposium on Reproductive Physiology of Fish, Wageningen, The Netherlands, 2-6 August, 1982. Compiled by H. J. Th. Goos and J. J. Richter. Pudoc, Wageningen. pp. 164- 173. HUNTER, G. A., E. M. DONALDSON, E. T. STONE,and H. M. DYE. 1978. Induced ovulation of female chinook salmon (Oncorhynchus tshawytscha) at a production hatchery. Aquaculture, 15: 99- 1 12. LIN,H-R., C. PENG,L-Z. Lu, X-J. ZHOU,G. VANDERKRAAK, and R. E. PETER.1985. Induction of ovulation in the loach (Paramisgurnus dabyranus) using pimozide and [D-~la~,~ro"-ethylamidelLHRH. Aquaculture, 46: 333-340. J-Z. LIANG, C. PENG,G-Y. Lr, L-Z. LIN,H-R., G. VANDERKRAAK, Lu, X-J. ZHOU,M-L. CHANG, and R. E. PETER.1986. The effects of LHRH analogue and drugs which block the effects of dopamine on gonadotropin secretion and ovulation in fish cultured in China. In Proceedings, International Symposium on the Aquaculture of Carp and Related Species. Edited by R. Billard. INRA Publications, Versaille, France. In press. PETER,R. E. 1 9 8 3 ~ .The brain and neurohormones in teleost reproduction. In Fish physiology. Vol. 9. Edited by W. S. Hoar, D. J. Randall, and E. M. Donaldson. Academic Press, New York. pp. 97- 135. 1983b. Evolution of neurohormonal regulation of reproduction in lower vertebrates. Am. Zool. 23: 685-695. SCOTT,A. P., J. P. SUMPTER, and P. A. HARDLMAN. 1983. Hormone changes during ovulation in the rainbow trout (Salmo gairdnerii Richardson). Gen. Comp. Endocrinol . 49: 1 28- 134. R. E. PETER,and B. BRETON. 1983. BILLARD. R., K. ALAGARSWAMI, SOKOLOWSKA, M.. R. E. PETER.and C. S. NAHORNIAK. 1985. he Potentialisation par le pimozide des effets du LHRH-A sur la effects of different doses of pimozide and [ ~ - ~ l a ~ . ~ r o ' - ~ - e t h ~ l secretion gonadotrope hypophysaire, 130vulationet la spermiation amidel-LHRH (LHRH-A) on gonadotropin release and ovulation in chez la carp commune (Cvprinus carpio). C. R. Hebd. Seances female goldfish. Can. J. Zool. 63: 1252- 1256. Acad. Sci. Ser. 3, 296: 181-184. M . , R. E. PETER,C . S. NAHORNIAK, and J. P. CHANG. BILLARD, R., P. REINAUD, M. G. HOLLENBECQ, and B, BRETON. SOKOLOWSKA. 1985. Seasonal effects of pimozide and des G ~ ~ ' O [ D -LHRH A~~~] 1984. Advancement and synchronisation of spawning in S~rlmo ethylamide on gonadotropin secretion in goldfish. Gen. Comp. gairdneri and S. trutta following administration ot' LRH-A cornEndocrinol. 57: 4.72-479. bined or not with pimozide. Aquaculture, 43: 57-66.


alone (Chang and Peter 1983b) . A stronger dopamine inhibitory tone in goldfish compared with coho salmon could account for this difference, although differences in pituitary sensitivity to LHRH-A could also have a role. Other studies on goldfish held at 20°C have shown that injection of pimozide together with LHRH-A results in a potentiation of LHRH-A action (Sokolowska et al. 1984). Recent studies on rainbow trout have shown that pimozide was more effective in stimulating gonadotropin release than LHRH-A; however, pimozide did not potentiate the response to LHRH-A (Billard et al. 1984). The difference between the results obtained in rainbow trout and those reported here probably related to the very low dose of LHRH-A (1 pg/kg) used in studies with rainbow trout, which causes only a transitory elevation of gonadotropin levels. Although dopamine inhibition may be involved in the regulation of gonadotropin secretion in coho salmon, it seems to play a less important role in comparison to the influence of dopamine in cyprinids. For example, injection of LHRH-A alone and in combination with pimozide were equally effective in inducing ovulation in coho salmon (Table I). In contrast, studies on goldfish (Chang and Peter 1983b; Sokolowska et al. 1984; Sokolowska, Peter, and Nahorniak 1985; Sokolowska, Peter, Nahorniak, and Chang 1985) and common carp (Billard et al. 1983; Lin et al. 1986) have shown that injections of pimozide and LHRH-A, but not LHRH-A alone, were necessary to induce ovulation. T o account for these species differences, it is necessary to consider the normal pattern of gonadotropin changes associated with ovulation in salmonids and cyprinids. In salmonids, a slow but gradual increase in plasma gonadotropin levels precedes ovulation (Fostier and Jalabert 1982; Scott et al. 1983; Van Der Kraak, unpublished observations), whereas a pronounced surge of gonadotropin is associated with ovulation in goldfish (Stacey et al. 1979) and commoil carp (Lin et al. 1986). In goldfish, the use of pimozide to block the effects of dopamine potentiates the action of LHRH-A, making it possible to mimic or exceed the normal preovulatory surge of gonadotropin and induce ovulation (Chang and Peter 1983b). These results suggest that the preovulatory surge of gonadotropin in goldfish is regulated by both a stimulation by G n R H and a release from dopamine inhibition on gonadotropin secretion. Unlike goldfish, the duration of the increase rather than the absolute magnitude of the increase in plasma gonadotropin levels is the important consideration for the induction of ovulation in coho salmon (Van Der Kraak et al. 1985). In this regard, the very prolonged effect of LHRH-A on gonadotropin secretion in preovulatory coho salmon underlines its effectiveness on the induction of ovulation. Although removal of dopamine inhibition is not necessary when using LHRH-A to induce ovulation in coho salmon, further tests are warranted to determine the effects of pimozide in combination with LHRH-A early in the spawning season when stimulation of a very long duration increase in gonadotropin secretion may be necessary to induce ovulation.

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CAN. J. ZOOL. VOL. 64, 1986


SOKOLOWSKA, M., R. E. PETER,C. S. NAHORNIAK, C. H. PAN,J. P. VANDER KRAAK, G., H. M. DYE, E. M. DONALDSON, and G. A. CHANG, L. W. CRIM,and C. WEIL. 1984. Induction of ovulation in HUNTER.1985. Plasma gonadotropin, 17P-estradiol and 17a,20Pgoldfish, Carassius auratus, by pimozide and analogues of LH-RH. dihydroxy-4-pregnen-3-one levels during luteinizing hormonereleasing hormone analogue and gonadotropin induced ovulation in Aquaculture, 36: 7 1-83. STACEY, N. E., A. F. COOK,and R. E. PETER.1979. Ovulatory surge coho salmon (Oncorhynchus kisutch). Can. J . Zool. 63: 824-833. of gonadotropin in the goldfish, Carassius auratus. Gen. Comp. H. M. DYE,and VANDERKRAAK, G., H. R. LIN,E. M. DONALDSON, Endocrinol. 37: 246-249. G. A. HUNTER. 1983. Effects of LH-RH and d e s - ~ l ~ ' O [ ~ - ~ l a ~ 1984. VANDERKRAAK,G., H. M. DYE,and E. M. DONALDSON. RH-ethylamide on plasma gonadotropin levels and oocyte maturaa m in i dadult e female coho salmon (Oncorhynchus kisutch). Gen. Effects of LH-RH and des ~ l ~ ' ~ [ ~ - ~ l a ~ ] ~ ~ - ~ ~ -one t h ~ ltion plasma sex steroid profiles in adult female coho salmon (OncorhynComp. Endocrinol . 49: 470-476. chus kisutch). Gen. Comp. Endocrinol. 55: 36-45.