Estrogen receptor beta (ERβ) mRNA and protein in serotonin neurons of macaques

This study used double in situ hybridization (ISH) to examine the colocalization of estrogen receptor beta (ERβ) mRNA in serotonin neurons of rhesus macaques (Macaca mulatta). In addition, immunocytochemistry (ICC) was used to examine the expression and regulation of ERβ protein in raphe neurons of the macaque midbrain. For double ISH, monkey specific riboprobes for ERβ incorporating radiolabeled-UTP and a riboprobe for the human serotonin reuptake transporter (SERT) incorporating digoxigenin were applied to midbrain sections from spayed rhesus macaques. ERβ mRNA hybridization signal was expressed in most cells containing SERT mRNA in the dorsal and median raphe and pons. There were also non-SERT neurons expressing ERβ mRNA. In addition, ERβ protein was detected with an affinity purified polyclonal antibody generated against a synthetic peptide corresponding to the D domain of human ERβ conjugated to bovine serum albumin (provided by Dr. Philippa Saunders, MRC, Edinburgh). Midbrain sections containing the dorsal raphe from spayed rhesus macaques with and without hormone replacement therapy were processed for ERβ immunostaining. ERβ protein was detected at a similar intensity and in a similar number of cells in the dorsal raphe neurons in all treatment groups. Thus, the expression of ERβ protein in the dorsal raphe was consistent with the expression of ERβ mRNA. In conclusion, ERβ mRNA is expressed by serotonin neurons and it is translated to protein. ERβ protein, like ERβ mRNA, is detected at similar levels in the presence or absence of ovarian hormones.