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In the last decade, research in our laboratories has focused on the effects of deafferentation of the mammalian chemosensory vomeronasal organ (VNX). Many different assays have been conducted and the results of some are briefly reviewed in this contribution, including the effects of VNX on neuroanatomical assessments using histochemistry (lectin binding) and immunohistochemistry (LHRH), male mouse and prairie vole ultrasonic vocalizations and hormone surges in response to cues from females, male mouse courtship and sexual behavior, territorial marking and inter-male aggression, the production of a puberty-altering substance found in mice, activation of reproduction in female voles (who generally do not exhibit estrous cycles) and maternal behaviors by female mice, including aggression directed toward intruder males. In some instances, the otherwise detrimental effects of VNX can be overcome by experience prior to deafferentation, especially in assays that are dependent upon expressions of behavior. In other situations, experience may have little impact on amelioration of the effects of VNX. The essential conclusions of this work focus our attention on reproductive physiology and behavior and a role for the vomeronasal organ in the perception of pheromones that modulate these functions.

The reproductive system of female prairie voles remains quiescent in the absence of stimulation from males; however, chemosignals from males are capable of at least partially activating female reproduction. In other species, the vomeronasal system mediates some of the reproductive responses of females to males. We found that surgical removal of the vomeronasal organ (VNX) from adult female prairie voles impeded reproductive activation in response to pairing with stud males: ovarian and uterine weights of VNX females paired with stud males for 24 or 60 hours were significantly less than those of normal (NORMAL) or sham-operated (SHAM) females. Furthermore, 8 of 9 NORMAL, 10 of 13 SHAM, but only 4 of 9 VNX females paired with stud males for 60 hours mated. VNX females, however, were still able to use chemosensory cues to locate food. Behavioral observations of females encountering stud males were similar for VNX, SHAM and NORMAL females. We conclude that vomeronasal chemoreception may be a primary component of reproductive activation in female prairie voles, presumably by mediating neuroendocrine responses to chemosignals.