Olfactory bulbs influence testosterone feedback on gonadotropin secretion in male hamsters on long or short...

Previous studies have shown that prepubertal olfactory bulbectomy will prevent the testicular regression associated with short photoperiod in golden hamsters. The gonadal regression which normally occurs in hamsters on short photoperiod is known to be due in part to an increased responsiveness of the reproductive neuroendocrine system to the negative feedback actions of testosterone on LH and FSH secretion. The present study tested whether the olfactory bulbs influence the feedback effects of testosterone on gonadotropin secretion. Twenty-four- to 26-day-old male golden hamsters were either olfactory-bulbectomized (BX) or sham-olfactory-bulbectomized. Eight weeks later, all hamsters were castrated, and one half of each group was placed in LD 10:14 (this was called week-8 of the study), while the other half was returned to long photoperiod (LD 14:10). Eight weeks following castration (week 0 of the study), all animals were implanted with silastic capsules containing 0, 4, 8 or 16 mm of testosterone. All hamsters were bled by cardiac puncture at -8, -4, 0, +2, +4, +6 and +8 weeks. The concentration of LH and FSH in these samples was then determined by RIA. BX completely prevented the negative feedback of testosterone on gonadotropin secretion in hamsters on either long or short photoperiod at all levels of testosterone tested in this study. In addition, there were seemingly steroid-independent effects of BX on gonadotropin levels in the castrated hamsters prior to testosterone replacement at weeks -4 and 0.(ABSTRACT TRUNCATED AT 250 WORDS)