Changes in Oestrogen Receptor-β mRNA Expression in Male Rat Brain with Age

Oestrogen has important roles not only in the regulation of reproductive function, but also with respect to other functions, such as cognition, emotion and cardiovascular regulation. Oestrogen acts mainly via its oestrogen receptor (ER), namely, ER alpha and ER beta in target tissues, including the brain. During ageing, the actions of oestrogen are altered in both females and males, raising the possibility that the expression level of ER may be altered with age. Age-related changes in ER expression in female rat brain have been well demonstrated with regard to reproductive ageing, whereas very little is known about the effects of age on the expression of ERs, especially ER beta, in males. In the present study, which aimed to elucidate the effects of ageing on ER beta expression in the male brain at the transcriptional level, we performed in situ hybridisation using young (10 weeks), middle-aged (12 months) and old (24 months) gonadally-intact male rats. We revealed a wide distribution of ER beta mRNA-positive cells throughout the brain, and found that the number of ER beta mRNA-positive cells was reduced in several brain regions in males with ageing. ER beta mRNA-positive cells were decreased with age in layer 6 of the cerebral cortex, hippocampal CA1/CA3 regions, the dorsal endopiriform nucleus, the medial septal nucleus, various subregions of the amygdala (central, lateral, anterior cortical and posterolateral cortical subnuclei), the anteroventral periventricular nucleus, the substantia nigra pars compacta, the raphe magnus nucleus and the locus coeruleus. These results suggest that ER beta expression in male rat brain decreases with age at the transcriptional level and that these ageing effects are region-specific.