Effect of 5,7-dihydroxytryptamine, ovariectomy and gonadal steroids on serotonin receptor binding in rat brain

Quantitative autoradiography was used to assess alterations in serotonin (5-HT) receptor binding in the hypothalamus and hippocampus following denervation with 5,7-dihydroxytryptamine (5,7-DHT), ovariectomy (OVX) and gonadal steroid manipulation. Seven days after 5,7-DHT injection, 5-HT1a receptor density was significantly increased in the ventromedial hypothalamic nucleus (VMN) of intact but not OVX female rats. Under these conditions 5-HT1b receptor density was unchanged in any brain region examined and 5-HT transporter binding was decreased in all 5,7-DHT injected animals. In addition, there was a significant interaction between OVX and 5,7-DHT for both the 5-HT1a receptor and the 5-HT transporter in the VMN, such that OVX inhibited the 5,7-DHT-induced increase in 5-HT1a receptors and attenuated the 5,7-DHT-induced decrease in 5-HT transporter binding. In a separate experiment the effect of gonadal steroid manipulation on 5-HT receptor binding was assessed. In female OVX rats, 5-HT1a receptor density was unchanged by estrogen or estrogen and progesterone administration. In male rats, castration significantly decreased 5-HT1a receptor density in the medial preoptic area. Estrogen and progesterone administration to female OVX rats increased the density of 5-HT1b receptors in the VMN, as compared to estrogen alone. The relationship of these results to the role of 5-HT in mediating lordosis behavior is discussed.