Chemical signals and vomeronasal system function in axolotls (Ambystoma mexicanum)

Abstract

We are studying the anatomy and physiology of the olfactory and vomeronasal systems in axolotls with the goal of determining the behavioral functions of these two chemosensory systems in aquatic amphibians. Our anatomical studies demonstrate that the vomeronasal epithelium of axolotls is much like that of other tetrapods. Other studies indicate that the projections from the olfactory and vomeronasal epithelia into the central nervous system are separate through several synapses, suggesting that these chemosensory systems serve different functions. Our electrophysiological experiments have not revealed striking differences in odorant responsivity between the olfactory and vomeronasal epithelia, but we are just beginning to work in this area and cannot draw yet strong conclusions about the relative quality or strength of odorant responses in these sensory epithelia. We have begun to show that odorant cues play a role in both foraging and in social behavior in axolotls; we hope that by combining neurobiological and behavior studies, we will be able to fully understand the ways in which chemosensory stimuli are processed to mediate behavior in axolotls. Given that separate olfactory and vomeronasal systems are present in amphibians and in amniotes, the vomeronasal system must have been present in the last common ancestor of these two groups, and this animal is now thought to have been fully aquatic (Panchen, 1991; Lebedev and Coates, 1995). An understanding of the function of the vomeronasal system in aquatic amphibians may help shed light on the factors that led to the evolutionary origin of the vomeronasal system.