Phylogenic Outline of the Olfactory System in Vertebrates

Abstract

ABSTRACT. Phylogenic outline of the vertebrate olfactory system is summarized in the present review. In the fish and the birds, the olfactory system consists only of the olfactory epithelium (OE) and the olfactory bulb (B). In the amphibians, reptiles and mammals, the olfactory system is subdivided into the main olfactory and the vomeronasal olfactory systems, and the former consists of the OE and the main olfactory bulb (MOB), while the latter the vomeronasal organ (VNO) and the accessory olfactory bulb (AOB). The subdivision of the olfactory system into the main and the vomeronasal olfactory systems may partly be induced by the difference between paraphyletic groups and monophyletic groups in the phylogeny of vertebrates.KEY WORDS: monophyletic, olfactory system, paraphyletic, phylogeny, vomeronasal system. J. Vet. Med. Sci. 73(2): 139-147, 2011 Olfaction is one of special senses of vertebrates, appears earliest among special senses in phylogeny, and remarkably contributes to the development of the neocortex in mammals [42,43,76]. In this context, studies on the phylogeny of olfaction in vertebrates are essential for the understanding of the evolution of the nervous system in mammals. On the other hand, although the large amount of data are accumulated on the morphology and function of the olfactory system in vertebrates, only a limited number of studies are published on the phylogeny of the olfactory system from a comparative anatomical point of view [7,33,34,41,48,88]. In the present review, therefore, we tried to describe our interpretation of the phylogeny of the olfactory system mainly on the basis of our morphological findings [44, 60-63, 65-67, 72-75, 79, 82-92, 100, 101] and generally accepted paleontological data [36,37,43,76]. COMPONENTS AND FUNCTIONS OF THE OLFAC-TORY SYSTEMThe olfactory system consists of the olfactory receptor organs and the primary and higher olfactory centers [30,43]. In the present review, the olfactory system must refer to the primary olfactory system consisting of the olfactory receptor organs and the primary olfactory center. The olfactory receptor organs are frequently represented by the olfactory epithelium (OE) and the vomeronasal organ (VNO) [11,15,23,24,33,50,60,[89][90][91][92]96], although the VNO is not an anatomically distinct structure in lower vertebrates and called as the vomeronasal sensory epithelium (VSE). It is generally accepted that the OE perceives the ordinary smells (odors) and the VNO the pheromones. By the way, the primary olfactory center is the olfactory bulb (OB). The OB is subdivided into the main olfactory bulb (MOB) and the accessory olfactory bulb (AOB) in several species [58,61,87]. In this case, the MOB receives projections from the OE, and the AOB from the VNO [4,5,32,62,79,87,97]. The OE and MOB constitute the main olfactory system, and the VNO and AOB the vomeronasal (accessory) olfactory system. The olfactory receptor organs and the primary olfactory center underwent diverse changes during phylogeny. The presence or absence of the VNO ...

Ultrastructural and Histochemical Properties of the Olfactory System in the Japanese Jungle Crow, Corvus macrorhynchos

“…In the Japanese jungle crow, the OE was thinner than the OE in mammals, composed of the SCs, RCs, and BCs, and possessed the nasal glands in the lamina propria. These histological features of the OE are similar to those in the ordinary birds [3,27], except for the domestic duck which has the goblet cells in the OE [12]. By PAS and alcian blue staining, it was shown that the nasal glands of the Japanese jungle crow contain a large amount of neutral and acid mucopolysaccharides.…”

“…The vomeronasal system detects species-specific substances, such as pheromones, received by the vomeronasal epithelium in the vomeronasal organ, and processes the information in the accessory olfactory bulb. In birds, however, the olfactory system consists of the OE and the olfactory bulb (OB), and completely lacks the components of the vomeronasal system [7,27].…”

Histological and Lectin Histochemical Studies on the Olfactory and Respiratory Mucosae of the Sheep

“…The mammalian olfactory mucosa is located in the posterior roof of the nasal cavity, where it mainly lines the ethmoturbinates and carries the receptor cells responsible for the detection and discrimination among odors of different substances [1, 2, 6, 15, 23, 24]. The olfactory mucosa consists of the olfactory epithelium and an underlying lamina propria.…”

Phylogenic Studies on the Olfactory System in Vertebrates

“…Asterisks (*) indicate extinct taxa.); and it seemed to be differentiated as the pheromone receptor [3, 26, 46]. The time and process of the differentiation of the VNO from the OE is an important problem in the phylogeny of olfaction in vertebrates [42]. This problem will later be discussed in this review.…”