Female snake sex pheromone induces membrane responses in vomeronasal sensory neurons of male snakes

The vomeronasal organ (VNO) is important for activating accessory olfactory pathways that are involved in sexually dimorphic mating behavior. The VNO of male garter snakes is critically important for detection of, and response to, female sex pheromones. In the present study, under voltage-clamp conditions, male snake VNO neurons were stimulated with female sexual attractiveness pheromone. Thirty-nine of 139 neurons exhibited inward current responses (reversal potential: -10.6 +/- 2.8 mV). The amplitude of the inward current was dose dependent, and the relationship could be fitted by the Hill equation. Under current-clamp conditions, application of pheromone produced membrane depolarizing responses and increases in firing frequency. These results suggest that the female pheromone directly affects male snake VNO neurons and results in opening of ion channels, thereby converting the pheromone signal to an electrical signal. The response to female pheromone is sexually dimorphic, that is, the pheromone does not evoke responses in VNO neurons of female snakes. An associated finding of the present study is that the female sex pheromone, which is insoluble in aqueous solutions, became soluble in the presence of Harderian gland homogenate.