Ultrastructure of the Olfactory Epithelium in a Flatfish, Barfin Flounder (Verasper moseri)

Abstract

ABSTRACT. In this study, we examined the olfactory epithelium (OE) of the barfin flounder by transmission electron microscopy. As in the case of the ordinary teleost, the OE of the barfin flounder had 3 types of olfactory receptor cells (ciliated olfactory receptor cell, microvillous olfactory receptor cell and crypt cell), 3 types of supporting cells (ciliated, microvillous and crypt supporting cells) and basal cells. Each type of OE cells in the barfin flounder had similar ultrastructure to that of the ordinary teleost. Crypt cell is the third type of olfactory receptor cell unique to fish, whose function is unclear. The barfin flounder may be a suitable material to study crypt cells because it has relatively abundant crypt cells in the OE.KEY WORDS: fish, olfactory epithelium, ultrastructure.J. Vet. Med. Sci. 72(6): 801-804, 2010 Many vertebrates have anatomically separated two olfactory organs: the olfactory epithelium (OE) and the vomeronasal organ (VNO). They detect general odorants and pheromones, respectively [1,3]. Although the OE is observed in all vertebrates, the VNO first appeared in amphibians during phylogeny. Since fish do not possess VNO, the OE of fish has been supposed to detect both general odorants and pheromones [9]. As in the case of other vertebrates, the OE of fish consists of the olfactory receptor cells (ORCs), supporting cells (SCs) and basal cells (BCs). In fish, there are three types of ORCs: the ciliated ORCs (cORCs), microvillous ORCs (mORCs) and crypt cells (CCs) [9]. In goldfish, the cORCs and mORCs have been shown to express genes homologous to the mammalian odorant receptors and vomeronasal receptors, respectively [2,10,11]. They are bipolar ORCs. On the other hand, CCs are the third type of ORCs unique to fish. Although CCs have been found in the OE of various kind of fish [4,8], their function in the olfaction is still unclear. In addition, SCs have been supposed to help ORCs in their olfactory function and BCs have been supposed to be the precursor cells of ORCs [9].The barfin flounder is a suitable material to study fish olfaction, because it is one of the macrosmatic fish, depends mainly on the olfaction for feeding, and is convenient to obtain as it is cultivated in a local research institute. Previously using the barfin flounder, we investigated the morphology of olfactory system by scanning electron microscopy, lectin histochemistry and immunohistochemistry [12][13][14]. In the present study, we examined the OE of the barfin flounder by transmission electron microscopy (TEM) to reveal the possible relationship between their ultrastructure and function.Three adult barfin flounders, about 30 cm in length, were obtained from the Iwate Fisheries Technology Center (Kamaishi, Japan). After euthanasia by decapitation, the olfactory epithelium was dissected out and fixed in 2% glutaraldehyde and 2.5% paraformaldehyde in 0.1 M cacodylate buffer (pH 7.4) overnight at 4C. Subsequently, it was postfixed in 1% osmium tetroxide for 2 hr at 4C, dehydrated in a graded series of e...

Phylogenic Studies on the Olfactory System in Vertebrates

“…In flatfish, the OE contains ciliated and microvillous olfactory cells, a special type of sensory cells, i.e., crypt cells, ciliated and microvillous supporting cells, and basal cells and lacks the associated glands [22, 45, 47]. We call this type of the OR the fish-type OE in this review.…”

Phylogenic Outline of the Olfactory System in Vertebrates

“…It has long been considered that the VNO is absent in the human as in the other higher primates, and only temporarily appeared as a primordium in the early fetal stages [63]. On the other hand, several authors reported the presence of the VNO in the human since the 1980s [40,56,79].…”

“…In addition, the crypt cells are occasionally encountered in several species. They are one of the receptor cells equipped with cilia and microvilli, and project their axons to the OB [63]. Their functional roles in the fish olfactory system are still unknown.…”