Effects of estrogen on the excitability of neurons projecting from the noradrenergic A1 region to the preoptic and anterior hypothalamic area

Estradiol benzoate administered to ovariectomized female rats significantly elevated the mean spontaneous firing rate and frequency of successful antidromic propagation into the somatodendritic spike and significantly reduced the strength of post-stimulus inhibition in presumed A1 noradrenergic neurons projecting directly to the preoptic and anterior hypothalamic area. The occurrence of both antidromic spikes and post-stimulus inhibition of the majority of these neurons was completely abolished by the injection of 6-hydroxydopamine but not by 5, 7-dihydroxytryptamine directly into the medial forebrain bundle.