Variations in binding of [ 3H]5-HT to cortical membranes during the female rat estrous cycle

Abstract

The binding of [ 3H]5-hydroxytryptamine ([ 3]-HT) to cortical membranes was examined in female rats during diestrus, proestrus and estrus. Serotonin binding was lowest during the early afternoon of proestrus and highest during the afternoon of estrus with diestrous values in between. The high estrous values were associated with a significant increase in B max and a decrease in K d . However, the increase in binding actually took place during the late afternoon of proesttrus, when there was a rapid increase in binding from noon to 18.00 h. Binding remained at this elevated level throughout the next day. There were no changes in the binding of [ 3H]ketanserin or [ 3H]spiroperidol to cortical membranes during the estrous cycle, so the differential binding of [ 3H]5-HT is most likely the result of variations in 5-HT 1 rather than 5-HT 2 receptors. These observations of changes in serotonin binding in a brain area nearly devoid of sex steroid receptors suggest that the hormonal fluctuations accompanying the female estrous cycle influence brain areas other than those classically thought to regulate neuroendocrine function.