Immunohistochemical colocalization of estrogen receptor-α and GABA in adult female rat hippocampus.

Background: Hippocampus is an important target for estrogen action. It is severely affected in patients of Alzheimer's disease. Much of the current research related to estrogen and brain function is focused in two directions.

Purpose: By attempting to lacalize localizing ERs in GABAergic neurons of the hippocampus we tried to test the hypothesis that the action of estrogen in maintaining the neuronal plasticity and more specially the spine density of pyramidal neurons is through GABAergic neurons.

Methods: The present study was planned to demonstrate the detailed immunoreactive (IR) distribution pattern of estrogen receptors (ER) in GABAergic neurons of hippocampus. The study was conducted in adult female Wistar rats in estrous phase. 30 µm thick cryostat sections of hippocampal region were obtained from perfusion fixed (with 4% buffered Para formaldehyde) adult female rats (n = 15). The sections were processed free- floating for immunolocalization using the PAP protocol. First they were immunostained for ER using, mouse monoclonal anti-ER-α antibody with DAB as chromogen. Subsequently the same sections were immunostained for GABA using rabbit monoclonal anti-GABA antibody respectively with 9 amino 3 ethyl carbazole (AEC) as chromogen.

Results: The results showed ER were colocalised in GABAergic neurons in all the subfields of hippocampus with obvious variations. In Cornua ammonis (CA) maximum co-localised neurons were seen in CA3 region.

Conclusions: The view is strengthened by our results as it was established through previous studies that the immediate target neurons of estrogen in hippocampus is the GABAergic neurons.