Transposition and Intermingling of Gαi2 and Gαo Afferences into Single Vomeronasal Glomeruli in the Madagascan Lesser Tenrec Echinops telfairi

Rodrigo Suárez,Jorge Mpodozis,Heinz Künzle,Aldo Villalón,Andrew Iwaniuk

doi:10.1371/journal.pone.0008005

Abstract

The vomeronasal system (VNS) mediates pheromonal communication in mammals. From the vomeronasal organ, two populations of sensory neurons, expressing either Gαi2 or Gαo proteins, send projections that end in glomeruli distributed either at the rostral or caudal half of the accessory olfactory bulb (AOB), respectively. Neurons at the AOB contact glomeruli of a single subpopulation. The dichotomic segregation of AOB glomeruli has been described in opossums, rodents and rabbits, while Primates and Laurasiatheres present the Gαi2-pathway only, or none at all (such as apes, some bats and aquatic species). We studied the AOB of the Madagascan lesser tenrec Echinops telfairi (Afrotheria: Afrosoricida) and found that Gαi2 and Gαo proteins are expressed in rostral and caudal glomeruli, respectively. However, the segregation of vomeronasal glomeruli at the AOB is not exclusive, as both pathways contained some glomeruli transposed into the adjoining subdomain. Moreover, some glomeruli seem to contain intermingled afferences from both pathways. Both the transposition and heterogeneity of vomeronasal afferences are features, to our knowledge, never reported before. The organization of AOB glomeruli suggests that synaptic integration might occur at the glomerular layer. Whether intrinsic AOB neurons may make synaptic contact with axon terminals of both subpopulations is an interesting possibility that would expand our understanding about the integration of vomeronasal pathways.

Highlights

In most mammals, the establishment and maintenance of social and sexual behaviours depend on the detection of semiochemicals by the vomeronasal system (VNS)
The accessory olfactory bulb (AOB) is located at the dorso-caudal extent of the main olfactory bulb (MOB) (Figure 1A)
The AONe is a narrow band of densely packed cells, caudal to AOB granular cells, while the AONc prolongs caudally into the frontal cortex (FrCx), in a transition zone that has been referred to as the sulcal cortex [36]

Summary

Introduction

The establishment and maintenance of social and sexual behaviours depend on the detection of semiochemicals by the vomeronasal system (VNS). Its neuroepithelium contains two spatially segregated populations of sensory neurons, each co-expressing either V1R receptors and Gai protein or V2R receptors and Gao protein, that send projections to distinct portions of the accessory olfactory bulb (AOB). Gai2-expressing axons end in glomeruli located exclusively in the rostral half of the AOB, while Gao-axons end in glomeruli of the caudal half of the AOB [1,2,3,4,5,6,7]. The dichotomic segregation of vomeronasal pathways into the AOB has been described in opossums [1], rabbits [8] and rodents [4,9,10], and was initially thought to represent a common feature of the mammalian VNS [11]. Later reports showed that the V2R-Gao pathway was absent in primates, shrews, goats, cows, horses, and dogs [12,13,14,15]

Objectives

Methods

Results

Conclusion