ERs are generally found in the cell membrane, cytosol as well as in the nucleus and mitochondria of both neuronal and non-neuronal cells and thus exert their respective biological functions accordingly. ERs that are present both in the cytosol, as well as in the nucleus are classified as class I nuclear steroid receptors [32]. E2 exerts its biological function by binding to its specific ER localized in the cytoplasm. The heat shock proteins maintain the ERs in an inactive state. Upon binding to E2, ER releases the bound heat shock proteins (HSP-90, HSP-56) and thereby exposes the corresponding nucleus localization sequence (NLS).