Abstract
Estrogen in the neonatal period plays a major role in the development of sexually dimorphic behaviors by acting through estrogen receptors (ERs). Though two types of ERs, ERα and ERβ, are identified, their role in the neonatal period to influence emotional and social behaviors in adulthood are largely unknown. Hence, we compared the effects of neonatal estrogen administration on the levels of anxiety, social investigation, and aggressive behaviors in ERβ knockout (βERKO) females with those in wild-type (WT) control mice. Female pups were administered with either estrogen benzoate (EB) or the vehicle (sesame oil) daily from postnatal day 1 through 3. All mice were, as adults, gonadectomized, EB substituted with a long-term release pellet, and individually housed. They were then tested for anxiety-related behaviors on the light-dark transition (LDT) test, social interaction with a novel same-sex mouse, and male-type aggressive behavior against olfactory bulbectomized male intruders in a resident-intruder paradigm. In WT mice, neonatal EB administration increased the levels of anxiety as seen by decreased time and distance traveled in the light compartment during LDT tests. Correspondingly, it also decreased interaction with a same-sex animal, and increased aggressive behavior. Lack of ERβ abolished the neonatal EB effect on anxiety and social interaction in adults, demonstrating the importance of ERβ in mediating the neonatal EB effect on these behaviors. (Supported by KAKENHI 17052001 to SO and the 21st Century COE Program to KX and SO.) [J Physiol Sci. 2008;58 Suppl:S93]
