Endocrine Abstracts

Chemosensory cues from receptive females produce the activation of the pituitary–testicular axis and facilitate a complex display of sexual behavior in male mice. Testosterone output in response to a receptive female and the pattern of sexual behaviour were investigated in male mice (n=190) of three inbred strains BALB/cLac, CBA/Lac and PT at puberty (45 days of age) and in adulthood (90 days). Sexually naive pubertal or adult male was exposed for 10 min to a receptive female separated by a plastic grill, which would not allow contact between them. Male behaviour was recorded by measuring the time the male spent at the grill and the number of approaches to it (sexual motivation). The grill was then removed and sexual behavior (the number of mounts, nasal and anogenital sniffing) was recorded for next 20 min. An increase in serum concentration and testicular content of testosterone was used as a reflexive endocrine index of the sensitivity to female pheromones. Testosterone was determined by the competition enzyme immunoassay. It has been shown significant effects of developmental and genetic factors on the testosterone response to sexual stimuli and sexual behaviour. The pubertal BALB/cLac males were characterised by the adult pattern of precopulatory behaviour and the evident testosterone respond to a female. The PT males showed the lowest level of behaviour towards a female and no testosterone response at both ages. The CBA/Lac’s demonstrated the developmental increase in endocrine responses and sexual behaviour, the highest number of mounts and the moderate testosterone respond to a female at adulthood. The patterns of sexual behavior and testosterone response to a receptive female in three inbred mouse strains demonstrate the genotype-related maturation of the pituitary–gonadal axis and neural circuits of sexual behavior, and provide confirmation that genetic differences are a major source of variation in reproductive maturation.