The sex bias in novelty preference of preadolescent mouse pups may require testicular Müllerian inhibiting substance.

Male mouse pups exhibit elevated preference for novelty relative to their sisters. The testes of pups secrete high levels of Müllerian inhibiting substance (MIS, anti-Müllerian hormone), with neurons being a target of this hormone. We report here that Mis+/+ male pups exhibit novelty preference, but their Mis−/− brothers and Mis+/+ sisters do not. This suggests that MIS is one of the determinants of “boy”-specific behavior.