ACTIONS OF TESTOSTERONE IN PREPUBERTAL AND POSTPUBERTAL MALE HAMSTERS- DISSOCIATION OF EFFECTS ON REPRODUCTIVE-BEHAVIOR AND BRAIN ANDROGENRECEPTOR IMMUNOREACTIVITY

This study was conducted to determine whether there is a increase in r esponsiveness to the activating effects of testosterone on male reprod uctive behavior during puberty in male golden hamsters and whether res ponsiveness to behavioral actions of testosterone is correlated with t he ability of testosterone to upregulate brain androgen receptor immun oreactivity (AR-ir). Sexually naive male hamsters were castrated at 21 or 42 days of age and implanted subcutaneously with a pellet containi ng 0, 2.5, or 5 mg of testosterone. One week later, males were given a 10-min mating test with a receptive female. Animals were euthanized 1 hr after the behavioral test, and blood samples and brains were colle cted. Plasma testosterone levels were equivalent in prepubertal and ad ult males that had been administered the same dose of testosterone. Ho wever, adult males exhibited more mounts, intromissions, and ejaculati ons than prepubertal males, demonstrating that postpubertal males are more responsive than prepubertal males to the effects of testosterone on sexual behavior. In both age groups, testosterone increased the num ber of AR-ir cells per unit area in several brain regions involved in male sexual behavior, including the medial preoptic nucleus (MPN), med ial amygdala, posteromedial bed nucleus of the stria terminalis, and m agnocellular preoptic nucleus (MPNmag). Surprisingly, testosterone inc reased AR-ir in the latter three regions to a greater extent in prepub ertal males than in adults. Thus, prepubertal males are more responsiv e to the effects of testosterone on AR-ir in these regions. In a separ ate experiment, a pubertal increase in the number of AR-ir cells per u nit area was found in both the MPN and MPNmag of intact male hamsters. These results indicate that a testosterone-dependent increase in brai n AR during puberty may be necessary, but is not sufficient, to induce an increase in behavioral responsiveness to testosterone. (C) 1997 Ac ademic Press.