Gonadotropin-releasing hormone modulates vomeronasal neuron response to male salamander pheromone

Abstract

Electrophysiological studies have shown that gonadotropin-releasing hormone (GnRH) modifies chemosensory neurons responses to odors. We have previously demonstrated that male Plethodon shermani pheromone stimulates vomeronasal neurons in the female conspecific. In the present study we used agmatine uptake as a relative measure of the effects of GnRHon this pheromoneinduced neural activation of vomeronasal neurons. Whole male pheromone extract containing 3 millimolar agmatine with or without 10 micromolar GnRH was applied tothe nasolabial groove of female salamanders for 45 minutes. Immunocytochemical procedureswere conducted to visualize and quantify relative agmatine uptake as measured by labelingdensity of activated vomeronasal neurons. The relative number of labeled neurons did not differ between the two groups: pheromone alone or pheromone-GnRH. However, vomeronasal neurons exposed to pheromone-GnRH collectively demonstrated higher labeling intensity, as apercentage above background (75%) as compared with neurons exposed to pheromone alone (63%, P, 0.018). Since the labeling intensity of agmatine within neurons signifies the relative activity levels of the neurons, these results suggest that GnRH increases the response of female vomeronasal neurons to male pheromone. ©the author(s), publisher and licensee Libertas Academica Ltd.