The specificity of the response of preoptic-septal area neurons to estrogen: 17α-estradiol versus 17β-estradiol and the response of extrahypothalamic neurons

The purpose of this study was to determine the specificity of the response of medial preoptic-septal neurons (mPOA-S) to microelectrophoresed 17β-estradiol hemisuccinate (17βE₂S). In vitro studies were conducted initially to determine the release of the labeled 17βE₂S from multibarrel glass micropipettes. Subsequently, an isomer of 17βE₂S, 17α-estradiol hemisuccinate (17αE₂S), was synthesized and purified. Thirty-six mPOA-S neurons from normal cycling female rats were tested with both 17βE₂S and 17αE₂S. Twelve of these units responded with inhibition to 17βE₂S, while none responded to 17αE₂S. Furthermore, fifty extrahypothalamic (cortical, hippocampal, thalamic) neurons were tested with 17βE₂S. The majority (N = 45) showed no response, three showed excitation and two inhibition to the microelectrophoresed steroid ester. These findings suggest that a specific receptor mechanism is responsible for the changes in mPOA-S unit activity, and that these effects may be important in the regulation of reproductive events.