Effects of Photoperiod and Androgen on Proopiomelanocortin Gene Expression in the Arcuate Nucleus of Golden Hamsters*

In golden hamsters, seasonal changes in day length act via a pineal-dependent mechanism to regulate feedback and behavioral effects of androgen. Endogenous opiates participate in photoperiod-ically regulated neuroendocrine functions, but the effects of androgen on expression of the gene encoding POMC, the precursor of b-endor-phin, have been controversial. We used quantitative in situ hybrid-ization to examine regulation of POMC messenger RNA (mRNA) by testosterone and to test the hypothesis that short day lengths act through the pineal gland to amplify POMC mRNA expression. We studied intact hamsters and castrates with or without androgen treat-ment held in long (14 h of light, 10 h of darkness) or short (5 h of light, 19 h of darkness) days for 10 weeks. POMC gene expression differed with rostral-caudal plane, photo-period, and surgical treatment (castration and testosterone admin