Morphological and immunohistochemical study of the rabbit vomeronasal organ

Abstract

The characterization of the rabbit mammary pheromone, which is sensed by the main olfactory system, has made this species a unique model for the study of pheromonal communication in mammals. This discovery has brought attention to the global understanding of chemosensory communication in this species. Chemocommunication is mediated by two distinct organs located in the nasal cavity, the main olfactory epithelium and the vomeronasal organ (VNO). However, there is a lack of knowledge about the vomeronasal system in rabbits. To understand the role of this system, an exhaustive anatomical and histological study of the rabbit VNO was performed. The rabbit VNO was studied macroscopically by light microscopy, and by histochemical and immunohistochemical techniques. We employed specific histological staining techniques (periodic acid‐Schiff, Alcian blue, Gallego's trichrome), confocal autofluorescence, histochemical labelling with the lectin Ulex europaeus agglutinin (UEA‐I), and immunohistochemical studies of the expression of the Gαi2 and Gαo proteins and olfactory marker protein. The opening of the vomeronasal duct into the nasal cavity and its indirect communication with the oral cavity through a functional nasopalatine duct was demonstrated by classical dissection and microdissection. In a series of transverse histological sections, special attention was paid to the general distribution of the various soft‐tissue components of this organ (duct, glands, connective tissue, blood vessels and nerves) and to the nature of the capsule of the organ. Among the main morphological features that distinguish the rabbit VNO, the presence of a double envelope, which is bony externally and cartilaginous internally, and highly developed venous sinuses stand out. This observation indicates the crucial role played in this species by the pumping mechanism that introduces chemical signals into the vomeronasal duct. The functional properties of the organ are also confirmed by the presence of a well‐developed neuroepithelium and profuse glandular tissue that is positive for neutral mucopolysaccharides. The role of glycoconjugates was assessed by the identification of the α1‐2 fucose glycan system in the neuroepithelium of the VNO employing UEA‐I lectin. The pattern of labelling, which was concentrated around the commissures of the sensory epithelium and more diffuse in the central segments, is different from that found in most mammals studied. According to the expression of G‐proteins, two pathways have been described in the VNOs of mammals: neuroreceptor cells expressing the Gαi2 protein (associated with vomeronasal receptor type 1); and cells expressing Gαo (associated with vomeronasal receptor type 2). The latter pathway is absent in most mammals studied. The expression of both G‐protein families in the rabbit VNO places Lagomorpha together with rodents and insectivores in a small group of mammals belonging to the two‐path model. These findings support the notion that the rabbit possesses a highly developed VNO, with many spe...

The vomeronasal system of the newborn capybara: a morphological and immunohistochemical study

“…1 and 4). This topography is only comparable to that described in rabbits 51 , where the organs rest over a prominence of the vomer bone. Two patterns of communication of the vomeronasal duct with the outside have been described.…”

Unique blood vasculature and innervation in the cavernous tissue of murine vomeronasal organs

“…Interestingly, the same authors noted an asymmetric muscle layer around the vomeronasal duct, namely the lateral thicker wall and medial thinner wall; the former displayed a very large amount of nerves with NOS-immunoreactivity (possibly cholinergic), while the latter showed a predominant NPY-immunoreactivity (possibly adrener-differing according to the location at the rostro-caudal axis. Based on figures presented in the literature, rabbits appear to possess the most developed vascular system, composed of grouped blood vessels with large diameters (Villamayor et al, 2018), being comparable to the mouse VNO examined in the present study. In contrast, animals like the opossum, cat, and wallaby do not have such advanced venous sinuses around non-sensory epithelium (Salazar et al, 1996;Poran, 1998;Schneider et al, 2008).…”

“…Stimulus substances must be forced into the organ by auxiliary devices rather than simple diffusion via the narrow entrance duct. The spongy tissue containing the developed vasculature is a kind of erectile tissue similar to the penis and functions to pump in or out the luminal contents of the vomeronasal duct (Meredith et al, 1980;Eccles, 1982;Villamayor et al, 2018).…”

The vomeronasal organ of wild canids: the fox (Vulpes vulpes) as a model

“…When Gαi2 and Gαo protein expression has been observed in rodents, such as the rat, two distinct zones were observed: an apical layer of neurosensory cells, which was immunopositive for anti-Gαi2 antibodies, and a basal layer, which was immunopositive to anti-Gαo antibodies (Halpern et al, 1998). In the fox, as in the rabbit (Villamayor et al, 2018), two distinct interspersed patterns were observed for the immunopositivity of both Gα proteins in the fox, which may be associated with two distinct subpopulations of neuroreceptor cells in the sensory epithelium of the VNO.…”