Effect of the pineal gland and melatonin on dopamine release from perifused hypothalamus of mature female carp during spawning and winter regression

Abstract

Epler P. 2005. Effect of the pineal gland and melatonin on dopamine release from perifused hypothalamus of mature female carp during spawning and winter regression. Acta Ichthyol. Piscat. 35 (2): 65-71.Background. Melatonin regulates various physiological and neuroendocrinological processes that occur rhythmically, and stimulates or inhibits endocrine activity of various body glands. This acts on the hypothalamic-pituitary-gonadal axis by synchronizing animals with their reproductive cycles. The proximity of melatonin receptors and dopamine and gonadoliberin production sites has led to a hypothesis that dopamine may be a link between melatonin and hypothalamic LHRH. Melatonin may have an indirect influence on animal reproduction through dopaminergic structures of the hypothalamus, but the mechanism involved remains unknown, also in fish, for this reason, the present experiment was conducted. The aim of the study was to determine the effect of melatonin on dopamine release from hypothalamic cells of mature female carp in vitro. Material and Methods. Hypothalami were perifused with a mineral medium containing melatonin (group 1), in the presence of implanted pineal glands (group 2), and with a pure mineral medium (control). Perifusion was 180 min long and samples of the effluent perifusate were collected at 15-minute intervals. Dopamine concentration in the medium was analysed radioenzymatically. The experiment was carried out in the summer during spawning and in the winter during regression. Results.The results indicate that melatonin inhibits the release of dopamine from hypothalamic cells. This effect was only noticeable in the experiment conducted during the spawning period. Conclusion. The present findings show that melatonin may have a role in the hypothalamic control of hypophyseal activity during the spawning period of carp.Key words: pineal gland, melatonin, dopamine, perifusion, carp, fish their reproductive cycles (Reiter 1991a, b, Zachmann et al. 1991.In looking for a link between the pineal gland and the hypothalamus, Zisapel and Laudon (1983) and Zisapel et al. (1985) showed that melatonin is able to inhibit dopamine secretion from the hypothalamic cells of the rat. The results of other studies, which showed that even picomolal concentrations of melatonin can inhibit dopamine release from the retina of birds and mammals (Cardinali et al. 1979, Dubocovich 1983, 1985, seemed to support this theory. Also in humans, the high nocturnal level of melatonin reduces dopaminergic activity in the hypothalamus (Rao and Mager 1987). In the brain of mammals, melatonin receptors are most abundant in the hypothalamus and in the anterior lobe of the pituitary gland, and much less abundant in the other parts of the brain (Weaver et al. 1991, Stankov et al. 1993. It is therefore conjectured that the hypothalamus acts as a functional link between melatonin and the endocrine system (Maywood et al. 1996). In the hypothalamus, the highest concentration of melatonin receptors is found in the medial eminence, next to the ...

Neuroendocrine control by dopamine of teleost reproduction

“…As proposed in a previous study, by this negative effect, melatonin would modulate LH secretion (Saligaut et al , 1998). A similar suggestion was put forward in a study in C. carpio , in which melatonin inhibited DA release in the hypothalamus both in vivo and in vitro (Popek et al , 2005, 2006).…”

Melatonin Induces Follicle Maturation in Danio rerio

“…In this regard, in the eel, the implant of melatonin induced a decrease in LHβ and FSHβ [45] while, an increase in LHβ secretion was found in croaker [46], in sea bass [47] and in cultured carp pituitary [42], showing the ability of this hormone to affect reproduction.…”

Melatonin receptors in the brain of the European sea bass: An in situ hybridization and autoradiographic study

“…Increasing evidence indicates that melatonin mediates the effects of photoperiod on several neuroendocrine functions in teleosts (Ekström and Meissl,1997; Mayer et al,1997; Falcón et al,2007b,2010). Thus, photoperiod manipulation, pinealectomy, and/or melatonin administration showed stimulatory or inhibitory effects on reproduction (Khan and Thomas,1996; Popek et al,2005; Bhattacharya et al,2007; Sébert et al,2008), feeding (Pinillos et al,2001; Rubio et al,2004; De Pedro et al,2008), and growth (Porter et al,1998; Mayer,2000; Falcón et al,2003; De Pedro et al,2008), acting at the brain, pituitary, and/or peripheral level. The distribution of the main neuroendocrine (gonadotrophin‐releasing hormone [GNRH], neuropeptide Y [NPY], and dopamine) and hypophysiotrophic systems has been elucidated previously in sea bass (Moons et al,1988,1992; Kah et al,1991; Batten et al,1993,1999; Cerdá‐Reverter et al,2000; Gonzalez‐Martínez et al,2001,2002,2004; E. García‐Robledo and J.A.…”