Seasonal and daily variations in the plasma gonadotropin II response to a LHRH analog and serotonin in Atlantic croaker (Micropogonias undulatus): evidence for mediation by 5-HT2 receptors.
The effects of serotonin (5-hydroxytryptamine; 5-HT) alone, and in combination with luteinizing hormone-releasing hormone analog (LHRHa), on plasma levels of maturational gonadotropin (GtH II) in the post-vitellogenic female and spermiating male Atlantic croaker were investigated during mid-light, late-light, mid-dark, and late-dark phases of the day-night (12 hr light: 12 hr dark) cycle. Although LHRHa stimulated GtH II secretion throughout the day-night cycle, maximal stimulation was observed during the mid-dark phase. Serotonin significantly potentiated LHRHa-induced GtH II secretion at all time points tested except during the late-dark phase. The plasma GtH II response to LHRHa was markedly reduced, and the response to 5-HT was abolished in regressed Atlantic croaker. Pretreatment of the fish with a 5-HT2 antagonist, LY 53,857 maleate, almost completely abolished the stimulatory effect of 5-HT on LHRHa-induced GtH II secretion, whereas a 5-HT1 antagonist, methiothepin mesylate, failed to influence the stimulatory effect of 5-HT on GtH II secretion. In addition, a 5-HT2 agonist, (+/-) DOI hydrochloride, potentiated the effect of 5-HT on basal and LHRHa-induced GtH II secretion, while a 5-HT1 agonist, m-chlorophenylpiperazine dihydrochloride, did not. The results clearly demonstrate time- and season-dependent stimulatory effects of LHRHa and 5-HT on plasma GtH II levels in Atlantic croaker. Moreover, the stimulatory effect of 5-HT appears to be mediated by 5-HT2 receptors in this species.
Khan
I A
IA
University of Texas at Austin, Marine Science Institute, Port Aransas 78373.
Thomas
P
P
D000818:Animals; D002940:Circadian Rhythm; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D006062:Gonadotropins / Q000097:blood*; D008297:Male; D010473:Perciformes / Q000097:blood*; D011985:Receptors, Serotonin / Q000502:physiology*; D012621:Seasons; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D006062:Gonadotropins; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D007987:Gonadotropin-Releasing Hormone