Bilateral removal of the olfactory bulbs (BX) inhibits the testicular regression associated with maintenance of golden hamsters on short photoperiod (10L:14D). The present study was done to examine the reproductive endocrine changes following BX of hamsters, to test whether BX increases gonadotropin secretion by enhancing the rate of metabolism of peripheral testosterone, and to determine whether BX inhibits the response to photoperiod by blocking chemosensory signals from conspecifics.BX resulted in a marked increase in tonic serum gonadotropin levels in pre-pubertal (23 days old) and adult hamsters maintained on long photoperiod (14L:lOD). Maintenance on 10L:14D inhibited gonadotropin secretion in BX hamsters, but this only reduced the previously elevated levels to those of the sham group on stimulatory photoperiod, and the testes therefore remained large.BX hamsters on 10L:14D had a higher post-castration increase in serum luteinizing hormone than sham-operated hamsters.Following testosterone replacement (20 mm Silastic capsules), BX animals had lower serum testosterone and higher serum folliclestimulating hormone levels than the sham group. BX hamsters had a shorter mean half-time for disappearance of testosterone from serum following removal of the capsule, but some animals in the sham group also metabolized testosterone rapidly. Isolation in cages receiving air filtered to remove pheromonal type molecules did not affect the rate or degree of testicular regression in response to short days.We conclude that the olfactory bulbs tonically inhibit gonadotropin release in golden hamsters on long or short photoperiod. The olfactory bulbs may facilitate the negative feedback of testosterone and may inhibit testosterone metabolism, but there were also steroid-independent effects. The influence of the olfactory bulbs on the hamsters' response to short days is apparently not related to chemosensory information from other hamsters.

Unlike seasonally breeding species such as the Syrian hamster, Sprague-Dawley laboratory rats do not normally respond to short photoperiod (6L:18D) with reproductive regression. However, removal of the olfactory bulbs (BX) unmasks a photoperiodic response in pre-pubertal rats so that blinding or short photoperiod results in an inhibition of reproductive hormone secretion and/or a delay in pubertal development. This is apparently mediated by pineal melatonin which inhibits gonadotropin and/or prolactin secretion, but the mechanism by which BX facilitates the response to photoperiod is not clear.Experiment I was performed to determine serum levels of reproductive hormones at frequent intervals following BX and/or maintenance on short days. Twenty-three-day old male rats were BX or underwent sham BX (SH). They were thereafter maintained on a 14L:lOD (long photoperiod) or 6L:18D photoperiod for the duration of the study. At 6 weeks following surgery, BX rats on either photoperiod had smaller testes than the SH groups. At week 8, the BX group on 6L:18D had smaller testes than the other three groups. There were transient reductions in serum luteinizing hormone and follicle-stimulating hormone in the BX rats on short photoperiod, but there were prolonged effects of BX decreasing prolactin levels in rats on long or short photoperiod. In SH rats, testosterone was elevated for weeks 6 through 10 of the study, and BX blocked this increase.Experiment II was performed to determine whether BX alters testosterone feedback on gonadotropin secretion. Twenty-three-day old male rats were BX or underwent SH operation and were then returned to a room on 14L:lOD. Six to 8 weeks later, all animals were castrated and placed on 6L:18D or returned to 14L:lOD. Eight weeks following castration, the rats were implanted with Silastic capsules containing 0, 10, 20 or 40 mm testosterone. The post-castration increase in serum luteinizing hormone and folliclestimulating hormone was lower in the BX khan SH rats. In long photoperiod, serum luteinizing hormone and follicle-stimulating hormone were often lower in the BX rats receiving no testosterone replacement or lower doses of testosterone than in the SH group receiving similar capsules. Maintenance on short photoperiod increased the responsiveness to testosterone so that even the rats receiving low doses of testosterone had very low luteinizing hormone and follicle-stimulating hormone levels whether they were SH or BX.In summary, BX rats on long or short photoperiod had lower serum prolactin and testosterone levels than the comparable SH group and BX inhibited the post-castration increase in gonadotropin secretion. The data therefore suggest that the olfactory bulbs tonically enhance reproductive hormone secretion (especially around the time of pubertal development).Golden hamsters undergo marked seasonal variations in reproductive competence (1-3). The inhibition of gonadotropin secretion associated with winter-like photoperiods is induced by pineal melatonin, which acts in large part b...

A radioimmunoassay system for measuring serum prolactin in rats was tested for its ability to measure serum prolactin concentrations in male deermice (Peromyscus maniculatus bairdii)• Preliminary assays showed that this system could be used in mice and that it had a sensitivity of 5 to 10 ng/ml. Serum prolactin was then measured at various times throughout the day to determine if a circadian rhythm existed in male mice. The results of this study indicated a single peak in serum prolactin concentrations occurred at 9*00 P.M., one hour prior to the end of the dark cycle. This study suggests that blood samples taken for prolactin analysis should be taken either at the end of the light cycle or the start of the dark cycle. It was found that serum prolactin concentrations were constant during this period. A study was done to determine pre and post puberty concentrations of serum prolactin and to determine if any correlation existed between these prolactin concentrations and the growth of the reproductive system in male mice. Serum prolactin was measured in groups of males from 10 to 90 days of age and compared with changes in body weight, testis weight, seminal vesicle weight and adrenal gland weight of males during the same age span. A significant positive correlation was found between serum prolactin and testis weight, seminal vesicle weight.and adrenal gland weight between the ages of 10 and 90 days.