in adult female rat hippocampus

have shown that the density of dendritic spines in the intact rat hippocampus undergoes marked variations during estrous cycle. A higher density of dendritic spines coincides with high levels of estrogen.10 Ovariectomy resulted in decrease in Cor-nua Ammonis (CA1) cell dendritic spines and it was prevented with estradiol treatment.11–13 One study showed that estradiol increases dendritic spine density by reducing GABA neurotrans-mission in hippocampal neurons14, thereby suggesting that the spine producing effects of estradiol in hippocampal pyramidal cells are possibly mediated by changes in inhibitory interneu-ronal synaptic efficacy that is lowering of GAD and thus GABA production. Keeping in view the above mentioned reports, the present study was planned to do co-localization immunohistochemi-cal studies to ascertain whether the two IRs are expressed in the same neurons. By attempting to lacalize ERs in GABA ergic neurons of the hippocampus we tried to test the hypothesis that the action of estrogen in maintaining the neuronal plastic-ity and more specially the spine density of pyramidal neurons is through GABAergic neurons. The review of literature has revealed that till date no in-vivo studies have been done or reported on the detailed distribution pattern of ER-α in GABAergic neurons of hippocampus. Methods 15 adult female Wistar rats (body wt. 200-210 g) in estrous phase of the estrous cycle (vaginal smears tested positive for cornified epithelial cells), housed in the Central Animal Facility of the All India Institute of Medical Sciences with 12 hrs light/dark photoperiod and ad libitum access to food and water, were anesthetized with Sodium Pentobarbi-tal (50 mg/kg.wt.i.p) and perfused transcardially with 4% Paraformaldehyde in 0.1 M Phosphate buffer (pH 7.4). Brain