Electrophysiological Characterization of Chemosensory Neurons from the Mouse Vomeronasal Organ

The mechanism of sensory transduction in chemosensory neurons of the vomeronasal organ (VNO) is not known. Based on molecular data, it is likely to be different from that mediating sensory transduction in the main olfactory system. To begin to understand this system, we have characterized the electrophysiological properties of dissociated mouse VNO neurons with patch-clamp recording. Sensory neurons were distinguished from nonsensory neurons by the presence of a dendrite, by immunoreactivity for olfactory marker protein, and by the firing of action potentials. The resting potential of VNO neurons was approximately -60 mV, and the average input resistance was 3 Gomega. Current injections as small as 1-2 pA elicited steady trains of action potentials that showed no sign of elicited steady trains of action potentials that showed no sign of adaptation during a 2 sec stimulus duration. The voltage-gated conductances in VNO neurons are distinct from those in olfactory neurons. The Na+ current is composed of two components; the major component was TTX-sensitive (Ki = 3.6 nM). The outward K+ current activates at -30 mV with kinetics 10 times slower than for K+ currents in olfactory neurons. The Ca2+ current is composed of at least two components: an L-type current and a T-type current that activates at -60 mV and is not found in olfactory neurons. We find no evidence for cyclic nucleotide-gated channels in VNO neurons under a variety of experimental conditions, including those that produced large responses in mouse olfactory neurons, which is further evidence for a novel transduction pathway.