Gonadal hormones and the induction of intraspecific fighting in mice.

Recent data pertaining to the influence of gonadal hormones upon intraspecific fighting behavior of mice are reviewed. Contrary to previous findings, exposure to testosterone during the neonatal period of development is not necessary for the activation of fighting later in life by testosterone treatment provided that the adult treatment regime is chronic. Rather than 'organizing' the central nervous system, neonatal exposure to testosterone appears to render it more 'sensitive' to the aggression-activating property of that steroid; animals exposed to it early in life fight more quickly following the commencement of adult testosterone treatment. Other data have revealed that the position in utero of female fetuses relative to males determines to a significant extent the sensitivity of the adult female to testosterone. The responsiveness to the hormone of females contiguous to two male fetuses is enhanced. And finally, although estrogen does not activate fighting in normal adult females, it will do so if the female has been administered either estrogen or testosterone during early life. Females exposed to low levels of estrogen as neonates also will display aggression in adulthood when estrogen titres normally are high. These data suggest that for normal female-like behavior to develop, it is essential that the neonatal ovary be relatively quiescent.