Retention of masculine sexual behavior following castration in male B6D2F1 mice

The reduction of masculine sexual behavior following castration varies widely among genotypes. In contrast to the loss of sexual behavior by castrated males of other strains, males of the B6D2F1 genotype retain the ejaculatory reflex for many weeks after castration. The present study examined this retention phenomenon. Masculine sexual behaviors were measured before and after castration or sham operation in male C57BL/6J, DBA/2J, and B6D2F1 mice. Castrated C57BL/6J and DBA/2J males showed a rapid decline in copulatory behavior. In contrast, 30% of the B6D2F1 males continued to ejaculate 25 weeks after castration. Regardless of whether or not sexual behaviors were retained, levels of plasma testosterone and hypothalamic nuclear estrogen receptors were reduced by castration. These results suggest that the intra- and inter-strain differences in the retention of sexual behavior following castration are not due to differences in levels of steroid hormones. Further, some B6D2F1 males retain the ability to copulate in the absence of gonadal hormone levels required for the maintenance of sexual behavior in other genotypes.