Neuroendocrine changes in male hamsters following photostimulation

Publisher Website
Google Scholar
Abstract
Transfer of gonadally regressed male golden hamsters from a short (5 L:19 D) to a stimulatory (14 L:10 D) photoperiod elicits, within 24 hr, significant changes in hypothalamic dopamine, serotonin, and possibly norepinephrine metabolism. Hypothalamic LHRH content was significantly elevated in short‐photoperiod animals, but within 24 hr of transfer to a 14:10 photoperiod, LHRH declined to levels not different from those in hamsters maintained continuously in a long photoperiod. Plasma FSH levels were also significantly elevated within 24 hr of transfer, but increases in plasma LH were somewhat slower. Chronic treatment with the tyrosine hydroxylase inhibitor, α‐methyl tyrosine (αMPT), which inhibits catecholamine synthesis, blocked the effect of a stimulatory photoperiod on plasma FSH levels, while treatment of 5:19 hamsters with the catecholamine precursor, L‐dopa, mimicked the effects of photostimulation on plasma FSH levels. Testicular weights were not affected by αMPT or L‐dopa treatment for 1 week. From these data, it appears that endocrine events associated with photoperiod‐induced testicular recrudescence are under the control of hypothalamic neurotransmitters.