Genotype and retention of the ejaculatory reflex in castrated male mice.

Genotype proves to be an important factor affecting the retention of sexual responsiveness following castration. Male F1 hybrids between C57BL/6 females and DBA/2 males (B6D2F1) show very prolonged retention. Experiment 1 used a diallelic design using C57BL/6, DBA/2 and BALB/c strains and showed that heterosis per se is not an adequate explanation of the superior retention of the B6D2F1 genotype. Experiment 2 showed that neonatal injections of 100 mug TP to B6D2F1 male mice did not result in better retention of the ejaculatory reflex after castration in adulthood. B6D2F1 males from both experiments who exhibited the ejaculatory reflex for many months after castration went through a 'difficult period' in the first 10 to 12 postcastration weeks. During this time, ejaculation latency increased fourfold, and then returned to the original level. On the other hand, the proportion of males reaching the ejaculatory threshold during this period first declined then increased.