Antigonadal Actions of Olfactory and Light Deprivation. II. Effects of Pinealectomy or Melatonin Injections in Olfactory Bulb Deafferented or Bulbectomized Male Rats

Since olfactory bulb deafferentation (peripheral anosmia) potentiates the antigonadal effects of light deprivation, we studied a) the pineal involvement in this action and b) whether peripheral anosmia might increase the response to melatonin injections. Four‐week‐old male rats were used in two experimental series. The first included rats in which blindness + peripheral anosmia was associated with either pinealectomy or sham pinealectomy. In the second series, intact, olfactory bulb deafferented and bulbectomized rats received daily injections of either melatonin (50 μg) or the vehicle alone. In both experiments animals were killed at 10 weeks of age. The reduction in the weight of accessory sexual glands and prostates, as well as in the serum testosterone levels, induced by blindness + peripheral anosmia was fully prevented by pinealectomy, whereas body and pituitary weight reduction induced by the dual sensory deprivation were only partially prevented. Melatonin produced no effects in intact animals whereas in rats with either peripheral anosmia or bulbectomy it reduced the weight of body, accessory sexual glands, and prostates. Serum testosterone levels were not modified in any case with melatonin treatment. From these results we concluded that the antigonadal effects of blindness + peripheral anosmia are pineal‐dependent, that peripheral anosmia sensitizes the neuroendocrine reproductive axis to the antigonadal effects of exogenous melatonin, and that the reduction in the weight of testosterone‐dependent organs induced by melatonin in bulbectomized or deafferented animals, together with the normal serum testosterone levels observed, suggests peripheral actions of melatonin of possible antiandrogenic nature.