Interactions of pinealectomy and short-photoperiod exposure on the neuroendocrine axis of the male Syrian hamster.
The effect of pineal gland removal on neuroendocrine function of male Syrian hamsters housed under long (14 h light:10 h dark) or short (5 h light 19 h dark) photoperiod conditions was tested. In sham-operated, but not in pinealectomized, animals, exposure to the short photoperiod resulted in a significant reduction in testicular weight. Median eminence (ME), medial basal hypothalamus (MBH), and medial preoptic-suprachiasmatic (MPOA-SCN) norepinephrine (NE) turnover was significantly reduced in 5 L:19 D sham-operated animals as compared to 14 L:10 D sham-operated or 14 L:10 D pinealectomized controls. The effects of short photoperiod on ME and MPOA-SCN NE turnover were reversed by pinealectomy, but reductions in MBH NE turnover were not dependent on the presence of the pineal gland. Pineal-dependent decreases in MBH and increases in MPOA-SCN dopamine turnover were also observed after transfer of hamsters from long to short photoperiods. Both ME and MBH luteinizing hormone-releasing hormone (LHRH) levels were increased after short-photoperiod exposure, but pineal removal prevented these increases of LHRH levels only in the MBH of the 5 L:19 D hamsters. Levels of serotonin or its metabolite, 5-hydroxyindole-acetic acid, were not affected by pinealectomy and/or short-photoperiod exposure. We conclude that short-photoperiod-induced gonadal atrophy in the Syrian hamster is associated with pineal-dependent and pineal-independent changes in hypothalamic neurotransmitter turnover and hypothalamic LHRH content.
D000818:Animals; D006224:Cricetinae; D004298:Dopamine / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000032:analysis*; D007031:Hypothalamus / Q000378:metabolism*; D008027:Light; D008297:Male; D008647:Mesocricetus; D018377:Neurotransmitter Agents / Q000032:analysis*; D009638:Norepinephrine / Q000378:metabolism; D010507:Periodicity; D010870:Pineal Gland / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism
D018377:Neurotransmitter Agents; D012701:Serotonin; D007987:Gonadotropin-Releasing Hormone; D004298:Dopamine; D009638:Norepinephrine