“…What is the mechanism by which a previously unresponsive neuronal type becomes responsive? Although estrogens can act to alter gene transcription (McEwen et al, 1978), it is unlikely that this is the case in the present study because in the hippocampus, both ␣-and -estrogen receptors have been identified on interneurons and glial cells and not on dentate granule cells (Rainbow et al, 1982;L oy et al, 1988;Pelletier et al, 1988;Weiland et al, 1996;Kuiper et al, 1997;Li et al, 1997). Estradiol might act directly on membranes, altering their properties to induce glutamate release, thus increasing intraneuronal calcium, stimulating NMDA receptors, leading to the addition of dendritic spines (Parpura et al, 1994;Woolley and McEwen, 1994;K lintsova et al, 1995).…”