Olfactory bulbectomy prevents anti-gonadal effect of exogenous melatonin in male hamsters.

When male Golden hamsters are maintained on short days (less than 12.5 h of light/day) the testes gradually regress. This testicular regression is due to an inhibitory effect of pineal gland melatonin on gonadotropin secretion. A previous report from the author's laboratory has indicated that olfactory bulbectomy (BX) will prevent the testicular regression associated with short photoperiod. The present study examined whether BX would also prevent the testicular regression associated with exogenous melatonin (MEL) injections. Male Golden hamsters were BX or sham (SH) BX at 23-28 days of age and were maintained on 14:10 light-dark cycle. Six weeks following surgery, one half of each surgical group began receiving injections of melatonin (15 micrograms sc), whereas the other half was injected with vehicle at 1600 daily. The testes size of the SH group injected with MEL progressively decreased, whereas the testes of all other groups remained large. These results indicate that BX prevents the testicular regression associated with short photoperiod by interfering with the antigonadotropic effect of melatonin.