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
✍ Scribed by Khan, Izhar A. ;Thomas, Peter
- Publisher
- John Wiley and Sons
- Year
- 1994
- Tongue
- English
- Weight
- 710 KB
- Volume
- 269
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Abstract
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‐HT~2~ antagonist, LY 53,857 maleate, almost completely abolished the stimulatory effect of 5‐HT on LHRHa‐induced GtH II secretion, whereas a 5‐HT~1~ antagonist, methiothepin mesylate, failed to influence the stimulatory effect of 5‐HT on GtH II secretion. In addition, a 5‐HT~2~ agonist, (±) DOI hydrochloride, potentiated the effect of 5‐HT on basal and LHRHa‐induced GtH II secretion, while a 5‐HT~1~ agonist, m‐chlorophenylpiperazine dihydrochloride, did not. The results clearly demonstrate timeand 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‐HT~2~ receptors in this species. © 1994 Wiley‐Liss, Inc.