Direct effects of androgens on lateral hypothalamic neuronal activity in the male rat: II. A pressure ejection study

Direct excitatory effects of sex steroids on lateral hypothalamic-medial forebrain bundle (LHA-MFB) neurons have been demonstrated in a previous study using the microiontophoretic ejection of charged hormone derivatives. In the present study neuronal discharge frequency was recorded during the local pressure ejection of the physiologically active form of these hormones. Of 56 neurones studied, 12 increased in activity due to testosterone application. Twenty-eight of these cells were tested with both testosterone and estradiol. Five were activated by both hormones, 4 were specifically excited by 17 Beta-estradiol, 3 were specifically excited by testosterone, and 16 were unaffected. The short latency of neuronal responses and the efficacy of nanomolar hormonal concentrations suggest the existence of high affinity specific sites in the plasma membrane of responsive neurons. The physiological significance of these neurons is discussed.