17β-estradiol inhibits excitatory amino acid-induced activity of neurons of the nucleus tractus solitarius

The effects of 17β-estradiol (17βE2) on spontaneous and excitatory amino acid (EAA) induced nucleus tractus solitarius (NTS) neuronal activity were investigated by electrophysiological and immunohistochemical experiments in ovariectomized female Sprague-Dawley rats. Out of 62 NTS neurons tested, 42 were inhibited (68%) following iontophoretic application of 17βE2 in a current-dependent manner. The averaged firing rate decreased from 3.06±0.40 to 0.78±0.17 Hz. The inhibitory responses were rapid in onset (within 1 min) and variable in duration (2-4 min). The inhibitory effects of 17βE2 were blocked by simultaneously applied 17βE2 antagonist ICI182,780, but not by GABA antagonist, bicuculline and phaclofen. L-Glutamate, AMPA or NMDA enhanced the activity of 71, 73 or 69% of NTS cells tested, respectively. The excitatory effects of EAA were significantly inhibited in the presence of 17βE2. Fluorescent immunohistochemistry revealed that all subnuclei of the NTS contained high levels of estrogen receptors (ERs) immunoreactivity. These results suggest that 17βE2 inhibits spontaneous and EAA-induced NTS neuronal activity through 17βE2 activation of ERs.