J. Steroid Biochem. Molec. Biol. Vol. 39, No. 4B, pp. 661-669, 1991 096(k0760/91 $3.00+ 0.00 Printed in Great Britain. All rights reserved Copyright © 1991 PergamonPress plc CONSEQUENCES OF REMOVING THE VOMERONASAL ORGAN CHARLES J. WYSOCKI l* and JOHN J. LEPRI 2 mMonell Chemical Senses Center, 3500 Market Street, Philadelphia, PA 19104 and 2Department of Biology, University of North Carolina at Greensboro, Greensboro, NC 27412, U.S.A. Summary--In the last decade, research in our laboratories has focused on the effects of dcaffcrcntation of the mammalian chemoscnsory vomeronasal organ (VNX). Many different assays have been conducted and the resultsof some are brieflyreviewed in this contribution, including the effects of VNX on ncuroanatomical assessments using histochemistry (lectin binding) and immunohistochcmistry (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 cstrous cycles) and maternal behaviors by female mice, including aggression directed toward intruder males. In some instances, the otherwise detrimental effectsof VNX can be overcome by experience prior to dcaffcrentation,especiallyin assays that arc dependent upon expressions of behavior. In other situations, experience may have littleimpact on amelioration of the effectsof VNX. The essentialconclusions of this work focus our attention on reproductive physiology and behavior and a role for the vomcronasal organ in the perception of pheromones that modulate these functions. INTRODUCTION Guided primarily by their noses, mammals have been enormously successful in penetrating and adapting to a wide variety of environmental conditions over the past 75 million years. This impressive record of diversification and success must be at least partially due to the continued evolutionary refinement of chemosensory communication and its exploi- tation to influence the behavior and neuroendo- crine status of conspecifics via pheromones [cf 1]. Commencing with the seminal work of Winans and her colleagues [2, 3], much research on small mammals has repeatedly and convinc- ingly demonstrated the role of the chemo- sensory vomeronasal organ (VNO) in the perception of pheromones and in the modu- lation of hormonal and behavioral responses to these substances (for reviews, see Refs [4-7]). The extent to which humans share this chemosensory heritage with small mammals is the subject of other papers in this issue. In this contribution we review some of the research Proceedings of the International Symposium on Recent Advances in Mammalian Pheromone Research, Paris, France, 6-9 October 1991. Sponsored by the EROX Corporation. *To whom correspondence should be addressed. that has been conducted in our laboratories during the last decade. Work with the vomeronasal system of small mammals has explored the multifaceted interactions between different sensory systems in the nose, hormone titers in the brain and in the blood, and behaviors known to be influenced by chemical signals, e.g. territorial marking, aggression and reproductive physi- ology and behavior. Our general paradigm is to study the behavioral and/or neuroendocrine effects of pheromones and social interactions comparing animals which possess a VNO and those which do not. Many years ago, a pro- cedure was perfected for removing the VNO via an oral approach[8]. After enlarging the incisive foramen with a dental burr, the entire VNO can be removed (VNX). VNX spares the olfactory epithelium, but it may affect substance-P containing (trigeminal?) fibers [9] and a few luteinizing hormone releasing hor- mone (LHRH) immunoreactive nerve fibers and perhaps cell bodies presumably of nervus terminalis that reside within the VNO [10, 11]. Whether peripheral endings of nervus termi- nalis are sensitive to chemosensory stimuli is another matter [cf. 12]. In this paper, we will review some of the effects of VNX, beginning with a discussion of the importance and 661