Estrogen effects on arcuate neurons in rat. An in situ electrophysiological study

IN acute experiments, the effects of i.p. 17 beta-estradiol on the activity of arcuate neurons were studied in ovariectomized rats. 17 beta-Estradiol (100 mu g/100 g, i.p.) increased the spontaneous activity of the observed a rcuate neurons with a latency of 20-25 min. In some neurons spontaneous act ivity could be influenced by stimulation of the olfactory and somatosensory systems. Activation of the trigeminal system significantly increased the s pontaneous activity of the studied units, while stimulation of the accessor y olfactory bulb decreased it, both with and without 17 beta-estradiol trea tment. It is suggested that the 20-25 min latency of the 17 beta-estradiol effect is based not so much on membrane as on genomic mechanisms. This sugg estion is supported by immunocytochemical studies: 17 beta-estradiol treatm ent significantly decreased the number of GABA-positive axe-somatic synapse s in the arcuate nucleus. (C) 1999 Lippincott Williams & Wilkins.