Unit activity in the hypothalamic arcuate area in rats at different stages of the estrous cycle

Changes in sensitivity to dopamine in various stages of the estrous cycle were studied in rats by microiontophoretic application to single neurons of the hypothalamic region and recording unit activity. Most arcuate neurons during the first half of the day in proestrus were shown to respond to dopamine by activation, to correspond to the raised plasma estrogen level in this phase of the estrous cycle. During the second half of the day in proestrus, when the estrogen level is minimal, and in stage diestrus-2, of all the neurons recorded the great majority responded to dopamine by inhibition.