GONADAL-STEROIDS HAVE PARADOXICAL EFFECTS ON BRAIN OXYTOCIN RECEPTORS

Specific brain receptors for oxytocin have been described in several m ammalian species. The distribution of these receptors differs greatly across species and in the rat, receptor binding in specific brain regi ons appears to depend upon gonadal steroids. This study used in vitro receptor autoradiography to examine the effects of testosterone on oxy tocin receptor binding in the mouse forebrain. Three groups of male mi ce were compared: castrates treated with blank capsules, castrates tre ated with testosterone filled capsules, and intact males. Irrespective of steroid treatment, the distribution of oxytocin receptors in mouse forebrain differed markedly from patterns previously described in the rat. In addition to these species differences in receptor distributio n, testosterone had effects in the mouse which differed from the induc tion of receptors previously reported in the rat. In the mouse ventrom edial nucleus of the hypothalamus, binding in the untreated castrate m ales was approximately double that observed in either the intact or th e testosterone-treated castrates. In other regions of the mouse brain, such as the intermediate zone of the lateral septum, binding to oxyto cin receptors was increased with testosterone treatment. These results suggest that the brain oxytocin receptor varies across species not on ly in its distribution but also in its regional regulation by gonadal steroids. These apparently paradoxical changes in oxytocin receptor bi nding may result from either direct or indirect effects of gonadal ste roids in mouse brain.