Rd. Romeo et al., PHEROMONES ELICIT EQUIVALENT LEVELS OF FOS-IMMUNOREACTIVITY IN PREPUBERTAL AND ADULT MALE SYRIAN-HAMSTERS, Hormones and behavior (Print), 34(1), 1998, pp. 48-55
Male reproductive behavior in the Syrian hamster is dependent on both
pheromones from the female and the presence of gonadal steroid hormone
s. The pheromones are contained within female hamster vaginal secretio
ns (FHVS) and stimulate anogenital investigation and mounting by the m
ale. Administration of testosterone to castrated male hamsters facilit
ates anogenital investigation, mounts, and intromissions in adults, bu
t elicits only anogenital investigation in prepubertal males. One hypo
thesis for why the full complement of reproductive behaviors is not ac
tivated by testosterone in prepubertal males is that the neural proces
sing of pheromonal cues encountered during anogenital investigation is
different in juveniles and adults. In the present experiment, we inve
stigated the influence of sexual maturity on Fos expression in respons
e to FHVS in the male Syrian hamster. We predicted a greater increase
in Fos-immunoreactivity after exposure to FHVS within the neural circu
it mediating male reproductive behaviors in adult compared to prepuber
tal males. Intact adult and prepubertal males were exposed to either a
clean cotton swab or a swab containing FHVS. We found that, compared
to animals exposed to a clean cotton swab, both prepubertal and adult
males exposed to FHVS have a greater amount of Fos-immunoreactivity wi
thin several brain nuclei comprising the neural circuit mediating male
reproductive behavior. Furthermore, this Fos response was equivalent
in the two age groups. These results suggest that the inability of the
prepubertal male hamster to perform the full repertoire of male repro
ductive behaviors is not due to a lack of a neuronal activation in res
ponse to the pheromonal cues present in FHVS. (C) 1998 Academic Press.