Sex differences in expression of serotonin receptors (subtypes 1A and 2A) in rat brain: A possible role of testosterone

Sexual differences in the expression of messenger RNA and in the binding of serotonin receptors (subtypes 1A and 2A) were studied by in situ hybridiza tion and autoradiography {[H-3]8-hydroxy-2(di-n-propylamino)tetralin and [H -3]ketanserin binding} in the rat brain. Serotonin-1A receptor messenger RN A showed distinct expression patterns for female and male rats. Expression of serotonin-1A receptor messenger RNA was greater in males in subregions o f the hypothalamus and amygdala, and less in males in subregions of the hip pocampus. No significant differences in the distribution of serotonin-1A re ceptor binding sites were found between the sexes. Serotonin-2A receptor me ssenger RNA expression was comparable in males and females in all brain reg ions except the ventromedial hypothalamic nuclei, where lower levels were s een in females. However, the binding of serotonin-2A receptor measured with [H-3]ketanserin was significantly higher in females in all regions of the hippocampus. In a separate study, gonadectomy in males significantly increa sed serotonin-1A messenger RNA content in the cortex, hypothalamus, hippoca mpus, amygdala and dorsal raphe, and decreased serotonin-2A messenger RNA i n ventromedial hypothalamic nuclei only. Almost all gonadectomy-induced cha nges were reversed by concomitant administration of testosterone. Our data provide evidence for region-specific sex differences in serotonin receptor subtype 1A and 2A transcription and concentration in the rat brain , and further suggest a modulatory role of testosterone in serotonin (parti cularly subtype 1A) receptor expression. Gender and gonadal steroid effects on central serotonergic systems may underlie the reported sexual dimorphis ms in affective state regulation, response to psychopharmacological agonist s or pituitary adrenal activation.