Diversity of the vomeronasal system in mammals: The singularities of the sheep model

Abstract

The enormous morphological diversity and heterogeneity of the vomeronasal system (VNS) in mammals--as well as its complete absence in some cases--complicates the extrapolation of data from one species to another, making any physiological and functional conclusions valid for the whole Mammalian Class difficult and risky to draw. Some highly-evolved macrosmatic mammals, like sheep, have been previously used in interesting behavioral studies concerning the main and accessory olfactory systems. However, in this species, certain crucial morphological peculiarities have not until now been considered. Following histological, histochemical and immunohistochemical procedures, we have studied the vomeronasal organ (VNO) and the accessory olfactory bulb (AOB) of adult sheep. We have determined: (1) that all structures which classically define the VNO in mammals are present and well developed, providing the morphological basis for functional activity. (2) that, conversely, there is only a scant population of scattered mitral/tufted cells. One morphological consequence of both details is that the strata of the AOB in adult sheep are not as sharply defined as in other species; moreover, the small number of the mitral/tufted cells in the AOB may imply that the VNS of adult sheep is not capable of functioning in the way a well-developed VNS does in other species. (3) the zone to zone projection from the apical and basal sensory epithelium of the VNO to the anterior and posterior part of the AOB, respectively, typical in rodents, lagomorphs and marsupials, is not present in adult sheep.

Lectin Histochemical Studies on the Vomeronasal Organ of the Sheep

“…The precise location of these melanin pigments has yet to be established. The significance of these pigments is unknown at present; and as far as we know, such melanin pigments have never been reported in sheep [18,27,28] nor other ruminants: Angora goats [4], buffaloes [1] and cows [26].…”

“…Each type of cell had properties that have been already described for the cells of vomeronasal sensory epithelium in sheep [18,27,28] and other ruminant species: Angora goats [4], buffaloes [1] and cows [26]. Briefly, nuclei of the vomeronasal basal cells, receptor cells and supporting The non-sensory epithelium was lined by pseudostratified ciliated columnar epithelium with goblet cells.…”

“…Vomeronasal receptors are distributed along the sensory epithelium, which occupies the medial wall of the VNO [18,25,27]. The histological and histochemical features of the sheep VNO have been evaluated before by some authors: Kratzing [18] focused on the ultrastructure of the sheep vomeronasal sensory epithelium, while Salazar et al [27,28] studied the lectin binding patterns in the VNO with special reference to nerve bundles and blood vessels, respectively. However, reevaluation of the sheep VNO by histochemical and lectin histochemical techniques enabled us to compare the glycoconjugates content in the vomeronasal sensory and non-sensory epithelia and to build the base for our future study by discussing the differences there-in between various sheep breeds.…”

A detailed morphological study of the vomeronasal organ and the accessory olfactory bulb of cats

“…The best characterized VNS, that of the mouse, is composed of the VNO, the AOB, the vomeronasal amygdala, and the nerves and tracts that connect them (Halpern, 1987;Halpern and Martinez-Marcos, 2003). Although this model can be recognized in most macrosmotic mammals, variations are significant Meisami and Bhatnagar, 1998;Takami, 2002)-as is variation in the genes coding for mammalian vomeronasal receptors (Grus and Zhang 2005Rodriguez et al, 2005;Young et al, 2005Young et al, , 2010Yu et al, 2010)-and must be borne in mind in drawing conclusions from nonanatomical studies (Salazar et al, 2007;Salazar and Sá nchez Quinteiro, 2009). Such variability is in fact in consonance with the involvement of the VNS in pheromonal communication, since pheromones are by definition species-specific, and different species have different reproductive strategies and behavioral priorities (Brennan, 2006;Keverne, 2005).…”

“…In the case of the VNS, there is an urgent need for detailed determination of its characteristics in mammals other than rodents, since this system varies widely among species (Salazar et al, 2007). Indeed, in certain species its anatomical peculiarities suggest that it may be in the course of involution (Salazar and Sá nchez-Quinteiro, 2009), and that the vomeronasal organ (VNO) may end up projecting to the MOB.…”