Experiential and endocrine dependence of gonadotropin responses in male mice to conspecific urine.

Previous research has shown that a urinary pheromone of female mice acts via the vomeronasal organ of the accessory olfactory system to elicit rapid release of luteinizing hormone (LH) in conspecific males. Several experiments were conducted to examine the importance of sexual experience for gonadotropin responses in male mice to female urine, male urine, saline, or mixtures of these stimuli. Both sexually naive and sexually experienced male mice had significantly higher plasma LH levels after presentations of female urine than after presentations of male urine. However, sexual experience appeared to increase the reliability of the short-latency gonadotropin response to female urine relative to a sexually neutral component of urine such as sodium chloride, and male urine appeared to suppress spontaneous LH secretion episodes in both naive and sexually experienced males. Subsequent experiments with sexually experienced subjects demonstrated that male mouse urine is a powerful suppressant of LH release in other males. Specifically, female mouse urine mixed with male urine failed to elicit LH responses in male subjects, whereas female urine mixed with saline was highly effective. Urine obtained from castrated male donors was as potent as urine from intact males in suppressing the gonadotropin response to female urine. The suppressive activity in male mouse urine thus does not appear to be critically dependent on gonadal hormones. The existence of a potent stimulatory pheromone in female urine and a potent suppressive pheromone in male urine makes male mice an excellent model system for studying the neural regulation of LH secretion.