Androgen actions on central serotonin neurotransmission: relevance for mood, mental state and memory

Abstract

Sex steroids exert potent effects on mood and mental state in the human. Our previous experimental findings in female rats suggest that these effects may be mediated, in part, by the action of estrogen on the 5-hydroxytryptamine 2A receptor (5-HT 2AR) and serotonin transporter (SERT) in brain. Here we review our recent findings on the effect of acute (∼32 h) testosterone manipulation on central 5-HT 2AR and SERT in male rats. Castration decreased while testosterone or estrogen, but not 5α-dihydrotestosterone (5α-DHT), increased significantly the content of 5-HT 2AR mRNA and SERT mRNA in the dorsal raphe nucleus (DR) and the density of 5-HT 2AR and SERT binding sites in higher centers of the brain. The lack of effect of 5α-DHT, a potent androgen which cannot be converted to estrogen, suggests that the action of testosterone depends upon its conversion to estrogen by aromatase. This may also explain why estrogen, but not testosterone or 5α-DHT, increased the density of 5-HT 2AR binding sites in the caudate-putamen, a brain region where aromatase is scarce. The estrogen induction of SERT mRNA is most prominent in the rostral DR and this together with the correlation between sensitivity of DR serotonin neurons to estrogen and neurotoxic amphetamine derivatives provides a potential topochemical handle with which to investigate testosterone/estrogen regulation of SERT gene expression. These findings are discussed in relation to the possible role of interactions between sex steroids and serotonin mechanisms in mood disorders, schizophrenia and Alzheimer's disease.