Patch-Clamp Analysis of Gene-Targeted Vomeronasal Neurons Expressing a Defined V1r or V2r Receptor: Ionic Mechanisms Underlying Persistent Firing.

Kirill Ukhanov, Trese Leinders-Zufall and Frank Zufall: J Neurophysiol 98:2357-2369, 2007. First published Aug 22, 2007

The vomeronasal system has long been a focus of study in mammalian sensory physiology. In rodents, the vomeronasal organ (VNO) is responsible for detection and transmission of a wide variety of pheromonal cues that are critically involved in social and reproductive behavior (Brennan and Keverne 2004; Brennan and Zufall 2006; Dulac and Torello 2003; Spehr et al. 2006). In mice, the sensory epithelium of the VNO is segregated into at least two structurally and functionally distinct layers: an apical layer that contains sensory neurons (VSNs) expressing the G protein G i2 and members of the V1r family of vomeronasal receptors, and a basal layer that contains VSNs expressing G o and members of the V2r receptor family (Buck 2000; Halpern and Martı´nez-Marcos 2003; Mombaerts 2004;
Ryba and Tirindelli 1997). These distinct populations of VSNs have been hypothesized to detect and process different classes of chemical signals (Kimoto et al. 2005; Leinders-Zufall et al. 2000, 2004) and are likely to use different signal transduction mechanisms (Kelliher et al. 2006; Leypold et al. 2002). This dichotomy is maintained in the accessory olfactory bulb (AOB) where apical VSNs project their axons to the rostral part of the AOB, whereas basal VSNs innervate the caudal AOB (for reviews see Buck 2000; Dulac and Torello 2003; Mombaerts 2004). Although it is generally difficult to predict with certainty which layer of the VNO a given VSN belongs to because of the diffuse boundary between the zones (Leinders-Zufall et al. 2004; Martini et al. 2001), cells are clearly identifiable in
gene-targeted strains of mice in which individual VSNs express green fluorescent protein (GFP) under the control of a
known V1r or V2r receptor. Over the past decade substantial progress has been made toward understanding of the molecular logic and coding strategies in the mammalian vomeronasal system (Bozza et al. 2004; Del Punta et al. 2002a,b; Dulac and Torello 2003; Luo et al. 2003; Rodriguez et al. 1999). However, surprisingly little is known about the detailed biophysical properties of individual VSNs and how they transmit olfactory information to the AOB by spiking in response to sensory stimulation (Holy et al. 2000; Inamura et al. 1997, 2000; Leinders-Zufall et al. 2000, 2004). Earlier, dissociated mouse VSNs were used to investigate the major voltage-dependent conductances (Fieni et al. 2003; Liman and Corey 1996), and it was suggested that differences between voltage-dependent conductances in apical and basal VSNs may provide the initial basis for differences in excitability between the two types of VSNs in rodents. Recently, an acute mouse VNO slice preparation was used to measure and model the excitability of basal VSNs due to voltage-dependent Na and K currents (Shimazaki et al. 2006). Here, we sought to extend that work by characterizing the electrophysiological properties of both basal and apical mouse VSNs using transgenic mice in which VSNs express GFP under the control of either the V1rb2 or V2r1b receptor gene, and by focusing also on the voltage-gated Ca2 (Cav) conductances that are important for spike generation and maintenance of persistent firing in VSNs.

Xanya Sofra Weiss

Xanya Sofra Weiss