Sexually dimorphic effects of testosterone on preoptic area calcitonin gene-related peptide mRNA expression depend upon neuron location and differential estrogen and androgen receptor activation

Experiments examined activational. roles of gonadal steroids on the sexuall y dimorphic, calcitonin gene-related peptide-expressing neurons of the rat preoptic area. Gonadectomy of male rats followed by treatment with testoste rone, dihydrotestosterone, or estrogen demonstrated that the tonic suppress ive influence of testosterone on cellular levels of calcitonin gene-related peptide mRNA expression in the medial preoptic nucleus and anteroventral p eriventricular nucleus occurred through either ER- or AR-mediated mechanism s (P < 0.05). The gonadectomy of adult female rats demonstrated little toni c influence of ovarian steroids upon calcitonin gene-related peptide mRNA l evels. However, the administration of male levels of testosterone to ovarie ctomized rats resulted in reduced calcitonin gene-related peptide mRNA expr ession within the medial preoptic nucleus (P < 0.05) and, strikingly, a 3-f old induction in calcitonin gene-related peptide mRNA expression in the ant eroventral periventricular nucleus (P < 0.01). Testosterone's effects in th e medial preoptic nucleus and anteroventral periventricular nucleus of the female required both ER and AR activation. Dual labeling immunocytochemical studies revealed that less than 10% of calcitonin gene-related peptide neu rons in the male expressed ARs compared with approximately 50% in the femal e. These investigations reveal that sexually differentiated region- and ste roid receptor-specific mechanisms function in association with the sex diff erences in circulating gonadal steroids to maintain the sexually dimorphic nature of calcitonin gene-related peptide expression in the preoptic area o f the adult rat.