Estradiol Modulation of Oxytocin Binding in the Ventromedial Hypothalamic Nucleus of Male and Female Rats

It has been suggested that estradiol and oxytocin (OT) may interact as neuroendocrine components in the regulation of sexual behavior. In the present study the effect of estradiol benzoate (EB) treatment (50 micrograms/kg body weight/2 days) on [3H]-OT binding was evaluated in adult and 21-day-old gonadectomized male and female rat brains. Coronal sections through the ventro-medial nucleus of the hypothalamus (VMN) were analyzed in three different section planes. EB priming induced an increase in [3H]-OT binding in the VMN of both male and female rats. Greater binding site density and significant EB effects were found in the most caudal plane where the ventrolateral portion of the VMN is well defined at both ages. OT binding in the central amygdaloid nucleus was not affected by this treatment but higher binding levels were found in the most caudal sections irrespective of hormonal status or sex. No sex differences were detected in OT binding in the VMN of basal or EB-treated animals. These results suggest that a dose of EB which activates female sexual behavior in female but not in male rats is able to induce similar levels of OT binding in the VMN of animals of both sexes.