Lesions of the suprachiasmatic nucleus do not disturb sexual orientation of the adult male rat

An enlarged suprachiasmatic nucleus (SCN) has been found earlier in a group of homosexual men, as compared to heterosexual controls. In order to assess a possible relationship between the SCN and sexual orientation, the present study was undertaken to investigate whether the rat SCN might play a role with respect to the expression of sexual orientation. Sexual orientation was measured in partner preference tests as the percentage of time spent in the vicinity of sexually active male and female incentives, that were separated from the experimental animal by a wire mesh. The results show that established patterns of sexual orientation towards female incentives by the adult male rat are not influenced by SCN-lesions. Disturbances in circadian rhythmicity of activity in SCN-lesioned animals did not affect this conclusion.