Fig. 4.
Schematic representation of differences between the site of action of estrogenic and androgenic hormones on the SCN and its inputs. Upper panel shows ER-rich nuclei (gray) that project to the SCN, including the retina, the intergeniculate leaflet, and the dorsal raphe nucleus, via the median raphe. Lower panel shows AR-rich areas in the core SCN and also the dorsal raphe. Testosterone can be aromatized into estradiol and thus may have dual androgenic/estrogenic impacts on the system. The SCN regulates circadian timing in physiology and behavior by sending outputs to autonomic and neuroendocrine systems. The SCN core receives direct input from the retina, the intergeniculate leaflet, and the median raphe nucleus, providing resetting information from photic cues and from activity/exercise.