In the mammalian brain the expression of ERs was also mapped and it became apparently clear that both ER subtypes are differentially expressed in the brain [21]. Additionally, ER density is found to be higher in the hypothalamus than in the extrahypothalamic areas [21] and [22]. In addition, ERα and ERβ may be colocalized in cholinergic neurone in the basal forebrain of rat [23]. However, ERβ is highly expressed in the cortex of male and female rat brain [24] and hippocampus of rat brain [25].