Novelty seeking in periadolescent mice: sex differences and influence of intrauterine position

In rodents, beside basic sex differences, a certain degree of within-gender phenotypic variation can also be provided in utero by hormones from adjace nt fetuses. We investigated novelty-seeking behavior in two groups of male and female mice from know intrauterine position: 2M (between males) and OM (between females). Subjects were assessed during periadolescence (postnatal days 33-43), an ontogenetic phase, which is characterized by an elevated e xpression of this novelty-seeking behavior. Periadolescent mice underwent a familiarization session for 3 consecutive training days with one side of a two-chamber apparatus. On testing day 4, the opening of a partition, which allowed mice to freely move from the familiar compartment to a novel one, produced an increased behavioral arousal in all animals. marked sex differe nces were found, with females being in general more active than males, wher eas the latter showed significantly higher levels of novelty seeking than f emales. Uterine position failed to affect the profile of novelty preference in females, whereas within the male group 2M subjects expressed a marked p rofile of novelty seeking. The differential titers of sex hormones reported to characterize the OM and 2M condition early in fetal development are sug gested to account for the individual variability in the seeking for novelty within the male group during puberty. (C) 2001 Elsevier Science Inc. All r ights reserved.