Infant vocalization, adult aggression, and fear behavior of an oxytocin null mutant mouse

Previous studies have shown that oxytocin (OT)-deficient female mice produc ed by homologous recombination fail to lactate but exhibit normal parturiti on and reproductive behaviors. We examined the ultrasonic vocalizations of infant mice and the subsequent aggressive and fear behavior of adult mate O T knockout (OT-KO) mice. Infant OT-KO mice were less vocal than wild-type ( WT) control mice during separations from the mother and peers. Adult OT-KO males were generally more aggressive in isolation-induced and resident-intr uder tests of aggression and less fearful in the plus maze and acoustic sta rtle reflex tests than WT controls. Although the increase in tests of aggre ssion was robust for OT-KO males from obligate litters (progeny of homozygo us x homozygous crossings), the increase in aggression was reduced during t ests for OT-KO males derived from non-obligate mating (progeny of heterozyg ous x heterozygous crossings), suggesting that the OT-KO genotype was not, by itself, responsible for the changes in adult behavior. We conclude that the absence of exposure to OT during development was associated with abnorm alities in the development of emotional behavior. (C) 2000 Academic Press.