Changes in dopamine, norepinephrine and serotonin levels in the pituitary, telencephalon and hypothalamus during gonadal development of male Lutjanus argentiventris (Teleostei)

Abstract.

Biogenic amines are important in the regulation of certain aspects of teleost reproduction, but relatively little is known about variations in their levels in the nervous system during the reproductive cycle. The aim of this study was to investigate changes in the levels of dopamine (DA), norepinephrine (NE), serotonin (5-HT), the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) and the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the pituitary and brain (hypothalamus and telencephalon) of the adult male of the tropical marine yellow snapper Lutjanus argentiventris during the reproductive cycle (quiescent, prespawning and spawning periods). Gonad weight, gonad/body weight ratio and plasma-testosterone levels increased steadily throughout gonadal development, but 17β-estradiol levels did not vary significantly. Pituitary DA and DOPAC levels and the DOPAC/DA ratio declined with gonadal development, whereas hypothalamic DOPAC level and DOPAC/DA ratio increased. In the telencephalon, DA and DOPAC levels and DOPAC/DA ratio all peaked in the prespawning period; however, DA level was lowest in the spawning period, whereas DOPAC level and DOPAC/DA ratio were both lowest in the quiescent period. Telencephalic NE, 5-HT and 5-HIAA levels likewise all peaked in the prespawning period, and were lowest in the spawning period. Telencephalic 5-HIAA/5-HT ratio peaked in the quiescent period and was lowest in the spawning period. No significant variation was observed either in pituitary NE level or in hypothalamic NE, 5-HT and 5-HIAA levels. The present results indicate that males of L. argentiventris show a decline in pituitary DA activity during gonadal development. We discuss the possible involvement of biogenic amines in the regulation of GTH II secretion, through direct action on the pituitary or indirect modulation of gonadotrophin-releasing hormone neuron activity.