Oxytocin increases the density of high affinity α2-adrenoceptors within the hypothalamus, the amygdala and the nucleus of the solitary tract in ovariectomized rats

Oxytocin induces long-term changes in, for example, blood pressure, spontaneous motor activity and corticosterone levels in rats. Previous studies in male rats have suggested a role for α2-adrenoceptors within the central nervous system in these effects. The aim of the present study was to investigate if oxytocin treatment in female rats would influence α2-adrenoceptors within the hypothalamus, the amygdala and the nucleus of the solitary tract (NTS). For this purpose, female ovariectomized (OVX) rats were treated with oxytocin (1 mg/kg s.c.) or saline once a day for 10 days. Rats were decapitated 5 days after the last injection, and brains and plasma were collected. Quantitative receptor autoradiography for characterization of high affinity α2-adrenoceptor agonist binding and radioimmunoassay for corticosterone were performed. Oxytocin increased the Bmax values of the α2-adrenoceptor agonist [3H]UK14.304 binding sites significantly in all the analyzed areas (P < 0.05). Kd values were unchanged. Plasma levels of corticosterone were significantly decreased in the oxytocin-treated rats (P < 0.05). These findings are in further support of an interaction between oxytocin receptors and α2-adrenoceptors and show that oxytocin treatment may increase α2-adrenoceptor recognition probably leading to an increase in α2-adrenoceptor signaling in several parts of the brain.