Gross Morphology and Fine Structure of the Olfactory Organ of Rainbow Fish (Atheriniformes, Melanotaeniidae)

The olfactory organs of 6 rainbow fish species were studied, and were compared with those of closely related cyprinodonts. It has been found that, in contrast to cyprinodonts, the olfactory mucosa of rainbow fish is more conspicuously thrown up into folds. Their arrangement in parallel is considered a relatively primitive character of the organ. Electron microscopic investigations on Nematocentris maccullochi have shown that the sensory epithelium consists of basal, supporting, and two types of receptor cells, ciliated and microvillous. As in cyprinodonts the receptor cell cilia exhibit a basic 9 + 0 microtubular pattern. In Nematocentris the frequency of receptor cells, between 200,000 and 250,000 per mm², is lower than in cyprinodonts. It may be suggested that the lower density is compensated for by enlargement of the sensory area due to the folding. In addition to broad-surfaced dendritic membrane appositions found in both Nematocentris and cyprinodonts, contacts by means of dendritic spines are found only in the rainbow fish. The olfactory supporting cells of the latter are distinguished from those in cyprinodonts by more prominent lateral interdigitations, centrioles, and the higher number of vesicles associated with extensive Golgi complexes.     

Ultrastructure of cell types of the olfactory epithelium in a catfish,Heteropneustesfossilis (Bloch)

Transmission electron microscopical study of olfactory epithelium of a mud-dwelling catfish,Heteropneustes fossilis (Bloch) shows receptor, supporting, goblet and basal cells. The receptor cells are of ciliated and microvillous type. Both ciliated and microvillous receptor cells are provided with olfactory knob. The dendrite of all the receptor cells bears many longitudinally arranged microtubules. Occurrence of the rod cell and its function is quite debatable. Specialized juctional complexes between the receptor and adjacent cells are clearly noted. The supporting cells are both ciliated and nonciliated. The ciliated supporting cells are responsible for water ventilation in the olfactory chamber as well as in the inter-lamellar spaces. This facilitates better perception of odours by the receptor cells. In addition to providing mechanical support to other cells, the nonciliated supporting cells also have a secretory function which is evident from the present study. The different stages of maturity of goblet cells are well documented. The presence of white cells in the olfactory epithelium is a very rare finding.     

The Olfactory System in the Hagfish Myxine glutinosa

The apical part of the olfactory epithelium in Myxine glutinosa was investigated by optical and electron microscopy. This part of the epithelium consists of supporting cells and two types of olfactory receptor cells, i.e., ciliated receptor cells and microvillous receptor cells. The olfactory cilia have a 9 + 0 pattern of the microtubules, occasionally with one pair of the doublets dislocated towards the center of the cilium. Giant cilia were observed. The supporting cells bear microvilli and are rich in tonofilaments. The supporting cells also have a secretory function, their secretion consisting mainly of acid mucopolysaccharides. An asymmetrical type of desmosome was found between the olfactory receptor cells and the supporting cells.     

Cells resembling hair cells in developing rat olfactory and nasal respiratory epithelia

A hitherto ignored microvillous cell type, distinct from microvillous supporting cells and other microvillous cell types, was encountered in olfactory and respiratory epithelia of nasal turbinates of rat fetuses, near the transition between these two epithelia. The apex of the cell resembles the apices of vestibular hair cells. The cell has a cone-shaped bundle of microvilli, resembling the complex bundle of hair-cell stereocilia, accompanied by a cilium. Therefore we called this cell type the nasal hair cell. Cilium and microvilli seemed adhered. Cell numbers were very low, up to about 5 per turbinate. The cell's appearance is precocious compared to that of olfactory receptor and supporting cells. Also, while the apices of olfactory receptor and supporting cells and of ciliated respiratory cells underwent major morphological maturation during the developmental period from embryonic day 16 to day 21, the apical structures of the nasal hair cell only changed marginally from embryonic day 16, when they were first seen, through to at least embryonic day 21. The cell's location and precociously mature appearance suggests that it plays a special role in the development of nasal epithelia.     

High correlation between microvillous olfactory receptor cell abundance and sensitivity to pheromones in olfactory nerve-sectioned goldfish

1. To determine whether microvillous olfactory receptor cells mediate responses to pheromonal cues, the olfactory nerves of mature male goldfish were axotomized and both the olfactory and behavioral sensitivity of these animals to olfactory stimuli investigated after which the histological condition of their olfactory epithelia was determined. 2. Behavioral responsiveness to food odor returned within 2 weeks but responsiveness to sexually-active females (pheromones) took 4–10 weeks to return. 3. Electro-olfactogram recordings from the olfactory epithelium of axotomized fish found that olfactory responsiveness to amino acids and pheromones changed little during the first week subsequent to axotomy. However, olfactory sensitivity decreased rapidly during the second week. During the course of the third week, electro-olfactogram sensitivity to amino acids remained while exposure to pheromones evoked no recordable electro-olfactogram. During week 4, sensitivity to amino acids increased further, and weak sensitivity to some pheromones became evident. Further recovery of electro-olfactogram sensitivity to all odorants was slow and erratic over the next 6 months, particularly to the pheromones. 4. Histological examination of the olfactory epithelia of axotomized fish demonstrated that while ciliated receptor cells were present within 2 weeks, microvillous receptor cells took approximately 4 weeks to regenerate. 5. Together these data suggest that microvillous receptor cells mediate responsiveness to pheromones in this species. Accepted: 22 August 1996     

Crypt neurons express a single V1R-related ora gene

Both ciliated and microvillous olfactory sensory neuron populations express large families of olfactory receptor genes. However, individual neurons generally express only a single receptor gene according to the "one neuron-one receptor" rule. We report here that crypt neurons, the third type of olfactory neurons in fish species, use an even more restricted mode of expression. We recently identified a novel olfactory receptor family of 6 highly conserved G protein-coupled receptors, the v1r-like ora genes. We show now that a single member of this family, ora4 is expressed in nearly all crypt neurons, whereas the other 5 ora genes are not found in this cell type. Consistent with these findings, ora4 is never coexpressed with any of the remaining 5 ora genes. Furthermore, several lines of evidence indicate the absence of any other olfactory receptor families in crypt neurons. These results suggest that the vast majority of the crypt neuron population may select one and the same olfactory receptor gene, a "one cell type-one receptor" mode of expression. Such an expression pattern is familiar in the visual system, with rhodopsin as the sole light receptor of rod photoreceptor cells, but unexpected in the sense of smell.     

Diversity in the olfactory epithelium of bony fishes: Development, lamellar arrangement, sensory neuron cell types and transduction components

In this study we use a taxon-based approach to examine previous, as well as new findings on several topics pertaining to the peripheral olfactory components in teleost fishes. These topics comprise (1) the gross anatomy of the peripheral olfactory organ, including olfactory sensory neuron subtypes and their functional parameters, (2) the ultrastructure of the olfactory epithelium, and (3) recent findings regarding the development of the nasal cavity and the olfactory epithelium. The teleosts are living ray-finned fish, and include descendants of early-diverging orders (e.g., salmon), specialized descendants (e.g., goldfish and zebrafish), as well as the Acanthopterygii, numerous species with sharp bony rays, including perch, stickleback, bass and tuna. Our survey reveals that the olfactory epithelium lines a multi-lamellar olfactory rosette in many teleosts. In Acanthopterygii, there are also examples of flat, single, double or triple folded olfactory epithelia. Diverse species ventilate the olfactory chamber with a single accessory nasal sac, whereas the presence of two sacs is confined to species within the Acanthopterygii. Recent studies in salmonids and cyprinids have shown that both ciliated olfactory sensory neurons (OSNs) and microvillous OSNs respond to amino acid odorants. Bile acids stimulate ciliated OSNs, and nucleotides activate microvillous OSNs. G-protein coupled odorant receptor molecules (OR-, V1R-, and V2R-types) have been identified in several teleost species. Ciliated OSNs express the G-protein subunit G_αolf/s, which activates cyclic AMP during transduction. Localization of G protein subunits G_α0 and G_αq/11 to microvillous or crypt OSNs, varies among different species. All teleost species appear to have microvillous and ciliated OSNs. The recently discovered crypt OSN is likewise found broadly. There is surprising diversity during ontogeny. In some species, OSNs and supporting cells derive from placodal cells; in others, supporting cells develop from epithelial (skin) cells. In some, epithelial cells covering the developing olfactory epithelium degenerate, in others, these retract. Likewise, there are different mechanisms for nostril formation. We conclude that there is considerable diversity in gross anatomy and development of the peripheral olfactory organ in teleosts, yet conservation of olfactory sensory neuron morphology. There is not sufficient information to draw conclusions regarding the diversity of teleost olfactory receptors or transduction cascades.     

Fine structure of olfactory epithelium inSchizothoraichthys progastus McClelland andSchizothorax richardsonii Gray (Cyprinidae: Teleostei) from Garhwal Himalaya (India)

The olfactory epithelium of two closely related species of snowtrout—Schizothoraichthys progastus McClelland andSchizothorax richardsonii Gray (Subfamily: Schizothoracinae. family-Cyprinidae, Teleostei), from a perennial glacier-fed river Mandakini of Garhwal hills was studied by employing transmission electron microscopic method The olfactory lamella comprises two epithelia—anterior and posterior, with a stroma sandwiched in between. Both are strartified. The anterior one is thicker than posterior. InSchizothoraichithys progastus, the sensory part of epithelium has two types of receptor cells—ciliated receptor cells and rod cells whilst inSchizothorax richardsonii, there arc three types of receptor cells—ciliated receptor cells, microvillous receptor cells and rod cells in addition to sustentacular cells, basal cells and mucous cells. While inhabiting similar hillstream habitat, the differential ecological niches, feeding habits etc., account for the presence of different receptor cell types in these species, It implies the possible diversification at cellular and physiological levels so as to minimize the competition by using varied olfactory cues.     

Functional Morphology of the Olfactory Organ in Spinachia spinachia (L.) (Teleostei,Gasterosteidae)

The functional morphology of the olfactory organ in Spinachia spinachia (L.), which has only a single nare, was studied by light microscopy, scanning electron microscopy, and experimental investigations. It was shown that only the incoming water passes over the olfactory epithelium. The device for ventilating this olfactory organ is an accessory ventilation sac activated by respiratory pressure changes in the buccal cavity. This one-way water current over the olfactory epithelium in a monotrematous olfactory organ was found to be possible because of the morphology of the olfactory organ combined with movements of the lateral wall of the olfactory organ and the nasal tube during respiration. The olfactory epithelium is divided into irregular islets. Both ciliated receptor cells and microvillous receptor cells are present.     

Whole-cell response characteristics of ciliated and microvillous olfactory receptor neurons to amino acids, pheromone candidates and urine in rainbow trout.

Olfactory lamellae of teleosts contain two morphologically different types of olfactory receptor neurons (ORNs): ciliated ORNs (cORNs) and microvillous ORNs (mORNs). However, little is known about the functional difference between these two types of ORNs in fish olfaction. We isolated cORNs and mORNs using a Ca(2+)-free solution method from olfactory organs of the rainbow trout and examined their response characteristics to various odorants including fish pheromone candidates by whole-cell voltage-clamp techniques. Quadruple mixture of amino acids, single amino acids, steroids (analogues of DHP; 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one and ECG; etiocholan-3 alpha-ol-17-one glucuronide), prostaglandins (PGFs) and urine samples collected from immature and mature female fish were applied focally to olfactory cilia or microvilli using a multi-barreled stimulation pipette with a pressure ejection system. Inward current responses to odorants were recorded from both cORNs and mORNs at a holding potential of -60 mV. cORNs responded to the amino acid mixture, single amino acids, urine samples and ECG, whereas mORNs responded specifically either to the amino acid mixture or single amino acids. The response profiles of both cORNs and mORNs to various odorants varied widely. None of cORNs and mORNs responded to fish pheromone candidates, PGFs and DHPs. Androgen treatment of immature fish did not influence olfactory sensitivity of both cORNs and mORNs to the amino acid mixture and both urine samples. Amino acid and bile acid analyses by HPLC showed that both urine samples contained 35 amino acids (1-40 mM) and trace amounts of taurocholic acid and glycoursodeoxycholic acid. Our results suggest that cORNs are 'generalists' that respond to a wide variety of odorants, including pheromones, whereas mORNs are 'specialists', specific to amino acids, and also suggest that PGFs and DHPs are not pheromones for the rainbow trout.     

Structure and Development of the Olfactory Organ in the Garfish Belone belone (L.) (Teleostei,Atheriniformes)

Theisen, B., Breucker, H., Zeiske, E., Melinkat, R. 1980. Structure and development of the olfactory organ in the garfish Belone belone (L.) (Teleostei, Atheriniformes). (Institute of Comparative Anatomy, University of Copenhagen, Denmark; Anatomisches Institut, Universität Hamburg, and Zoologisches Institut und Zoologisches Museum, Universität Hamburg, Federal Republic of Germany.) — Acta zool. (Stockh.) 61(3): 161–170. The structure and development of the olfactory organ in the garfish Belone belone (L.) were studied by light and electron microscopy (SEM and TEM). The olfactory organ has the shape of an open groove with a protruding papilla. In embryos and early juveniles the groove is smooth and is provided with a continuous sensory epithelium. During ontogenesis the papilla develops and the composition of the epithelium is changed as areas of nonsensory epithelium appear and eventually separate the sensory epithelium into islets. In adults the sensory epithelium consists of supporting, basal, and two types of receptor cells, ciliated and microvillous. In juveniles also ciliated nonsensory cells are present. This difference can be correlated with differing locomotory habits of adults and juveniles. The receptor cilia show a 9 + 0 microtubular pattern while the nonsensory cilia have the general 9 + 2 pattern. Deviating dendritic endings were found and are considered an indication of ongoing cell dynamics.     

Ultrastructural studies on the epithelia of the olfactory organ of cyprinodonts (teleostei,cyprinodontoidea)

Summary The epithelia of the olfactory organ of two cyprinodontoid fish species were studied both by transmission and scanning electron microscopy. The relatively flat floor of the organ is covered by sensory and nonsensory epithelia. The latter is distributed in the form of bands or ridges separating distinct areas of sensory epithelium. Differences between the olfactory organs of the two species investigated related only to the topography and quantitative distribution of the epithelia. Their ultrastructural features are very similar. The nonsensory stratified squamous epithelium contains numerous goblet cells and surface cells provided with microridges. A hypothetical function of the microridges is discussed. The sensory epithelium consists mainly of basal, supporting, and two types of sensory cells, i.e., ciliated and microvillous receptor cells. The cilia exhibit a predominant 9+0 microtubule pattern. Both epithelia are covered by a mucus layer in which all surface structures seem to be embedded. The possible nature, origin, and movement mechanisms of the mucus are discussed.This work was supported by the Deutsche ForschungsgemeinschaftDedicated to Prof. Dr. med. W. Bargmann on the occasion of his 70th birthday     

Olfactory metamorphosis in the coastal tailed frog Ascaphus truei (Amphibia,Anura, Leiopelmatidae)

The structure of the olfactory organ in larvae and adults of the basal anuran Ascaphus truei was examined using light micrography, electron micrography, and resin casts of the nasal cavity. The larval olfactory organ consists of nonsensory anterior and posterior nasal tubes connected to a large, main olfactory cavity containing olfactory epithelium; the vomeronasal organ is a ventrolateral diverticulum of this cavity. A small patch of olfactory epithelium (the “epithelial band”) also is present in the preoral buccal cavity, anterolateral to the choana. The main olfactory epithelium and epithelial band have both microvillar and ciliated receptor cells, and both microvillar and ciliated supporting cells. The epithelial band also contains secretory ciliated supporting cells. The vomeronasal epithelium contains only microvillar receptor cells. After metamorphosis, the adult olfactory organ is divided into the three typical anuran olfactory chambers: the principal, middle, and inferior cavities. The anterior part of the principal cavity contains a “larval type” epithelium that has both microvillar and ciliated receptor cells and both microvillar and ciliated supporting cells, whereas the posterior part is lined with an “adult‐type” epithelium that has only ciliated receptor cells and microvillar supporting cells. The middle cavity is nonsensory. The vomeronasal epithelium of the inferior cavity resembles that of larvae but is distinguished by a novel type of microvillar cell. The presence of two distinct types of olfactory epithelium in the principal cavity of adult A. truei is unique among previously described anuran olfactory organs. A comparative review suggests that the anterior olfactory epithelium is homologous with the “recessus olfactorius” of other anurans and with the accessory nasal cavity of pipids and functions to detect water‐borne odorants. J. Morphol. 2011. © 2011 Wiley Periodicals, Inc.     

The Olfactory System in the Pacific Hagfishes Eptatretus stoutii,Eptatretus deani,and Myxine circifrons

In front of the olfactory organ in the northeastern Pacific hagfishes Eptatretus stoutii, E. deani, and Myxine circifrons there is a valve that may function to direct water in between the olfactory laminae. In Myxine circifrons the well developed valve is supposed to act alone, whereas the smaller valve in the two species of Eptatretus studied is supposed to act together with the horizontal extensions of the median olfactory lamina. No significant differences were found between the investigated species by ultrastructural examination. In the olfactory epithelium the supporting cells are provided with microvilli and generally contain a great amount of light secretory granules. Both ciliated olfactory receptor cells and microvillous olfactory receptor cells are present. The cilia show a 9 + 0 arrangement of the microtubules with a tendency for a dislocation of one pair of the microtubules toward the center of the cilium. These remarkable features of the olfactory receptor cells, not yet seen in other vertebrates, appear to be a character common to the myxinoid cyclostomes.     

中华须鳗嗅觉器官形态学观察

利用光学显微镜和扫描电镜观察了10尾不同体长中华须鳗嗅觉器官的结构.结果表明:中华须鳗嗅囊呈楔型;嗅囊膜和嗅囊腹面的透明膜共同围成嗅囊腔;嗅囊长径与眼径的平均比值为2.2倍;每侧嗅囊嗅板数变化范围在30～44之间;嗅板远轴端有一纤毛和嗅孔密集的舌状游离突;嗅板上皮纤毛密集,纤毛细胞表现为3种类型:纤毛感觉细胞、纤毛非感觉细胞和微绒毛感觉细胞;纤毛非感觉细胞和微绒毛细胞也出现在嗅囊壁.嗅板上大量的纤毛表明,中华须鳗嗅囊的水动力机制应属嗅板纤毛搅动型(isosmates).除观察到嗅囊壁表面有两种类型的微嵴外,还首次在嗅板上观察到一种呈荸荠状的杆状细胞.     

Scanning electron microscopic study of the olfactory epithelium of four coldwater hillstream teleosts from Garhwal hills (India)

This contribution deals with the scanning electron microscopic surface structure of olfactory epithelium in four hillstream teleosts from the glacialfed river Alaknanda in Garhwal Himalaya (UP, India). The closely related species—Schizothorax plagiostomus, Schizothorax richardsonii (both bottom dweller, bottom feeder, herbiomnivorous) andSchizothoraichthys progastus (column dweller, column feeder, carniomnivorous) reveal the predominance of different types of olfactory receptor cell types separately in their respective olfactory epithelium while the distinctly related speciesCrossocheilus latius latius with similar nature as first two (i.e. bottom dweller, bottom feeder, herbiomnivorous) displays the presence of more microvillous cells in the olfactory epithelium. Possibly, the occurrence of particular receptor cells in a fish species is related to the ecological and feeding behaviours with distinct mechanism of olfaction.     

Freeze-fracture study of the receptor membranes in the olfactory organ of Alburnus alburnus (Teleostei)

Summary Olfactory receptor molecules are assumed to be integral membrane proteins which may be visualized on fracture faces of the membrane as intramembrane particles (IMPs). In the present study, the plasma membrane of the receptor dendrites and ciliated epithelial cells in the teleost fish Alburnus alburnus were studied by freeze-fracture electron microscopy. The IMP diameters on the membrane P-faces of both receptor dendrites and ciliated epithelial cells ranged from 5 nm to 11 nm. The average IMP densities on membrane fracture faces of the ciliated and microvillous sensory dendrites were 3130±780 for the cilia, 2070±550 for the microvilli, 2390±1190 on the knob regions and 3050±1130/m on the lateral dendrite membranes. The IMP densities on the P fracture faces of the cilia and knob regions were compared with the densities found on the lateral membranes of each individual dendrite. The ratios ranged from 0.5 to 0.96 in the case of the cilia/lateral membrane and from 0.5 to 0.90 in that of the knob/lateral membrane, indicating that, in contrast to the average densities, it is the lateral membrane which has the higher IMP densities and not the cilia. The great variations in the average IMP densities, as well as the considerable variety of the ratios, may be explained by the maturation and turnover of the olfactory sensory neurons.     

The spatial distribution of ciliated and microvillous olfactory receptor neurons in the channel catfish is not matched by a differential specificity to amino acid and bile salt stimuli

The distribution of two receptor cell types, stellate microvillousand ciliated, was quantitatively examined in the sensory regionsof the olfactory lamellae of the channel catfish, Ictaluruspunctatus. Using scanning electron microscopy (SEM), these twocell types were seen to exhibit an incomplete segregation acrossthe sensory epithelium. The density of stellate microvillouscells was greatest in the dorso-medial portion of the sensoryregion of the lamella and markedly decreased ventrally and laterally.The ciliated cells were more numerous in the ventro-lateralportion of the sensory region and decreased in number dorso-medially.Multi-unit olfactory neural responses to amino acids and bilesalts were recorded from the dorso-medial and ventro-lateralportions of the sensory region. In both portions of the sensoryregion, L-cysteine, L-alanine and L-norleucine were highly stimulatory,while the sodium salts of cholic acid, taurocholic acid andtaurolithocholic acid (i.e., bile salts) were the least stimulatorycompounds tested. With the exception of L-norleucine, no significantdifferences were found in the responses from the dorso-medialand ventro-lateral portions of the sensory region for the compoundstested. These results indicate that in I. punctatus the responsespecificities of the microvillous and ciliated olfactory receptorcells are similar for amino acids and bile salts.     

Organization of olfactory system of the Indian major carp Labeo rohita (Ham.): a study using scanning and transmission microscopy

Catla catla, Labeo rohita, and Cirrhinus mrigala are important alimentary fish in India. Their reproduction (breeding) depends on season. The fish perceive external factors-stimuli and chemical signals through the olfactory system that plays the key role in the central regulation of reproduction. However, in the available literature, any electron microscopy data on organization of olfactory elements in these fish are absent. We have studied ultrastructure of the olfactory organ in male L. rohita by using scanning (SEM) and transmission electron microscopy (TEM). The olfactory organ consists of olfactory epithelium, a short nerve, and olfactory bulb. The organ has oval shape and consists of approximately 47-52 lamellae in adult fish and of 14-20 lamellae in fish at the stage of fingerling. These lamellae originate from the midline raphe. By using SEM, the presence of microvillar sensory and ciliated non-sensory cells in these lamellae is shown. By using TEM, a microvillar receptor cell is revealed, which has rough endoplasmic reticulum and Golgi apparatus towards the apical end. Basal cells are found at the base of the receptor cell; supporting cells are located adjacent to olfactory receptor neurons, while epithelial cells--in the non-sensory part of olfactory epithelium. Mast, blastema and macrophages cells are also found in the basal lamina. This work is the first publication on structural organization of olfactory system of the Indian major carp, which provides information about morphological and ultrastructural organization of olfactory system and opens new opportunities for study of chemical neuroanatomy, sensory signal processing, and nervous regulation of reproduction of the Indian major carp.     

Olfactory sensitivity to amino acids in the juvenile stages of the European eel Anguilla anguilla (L.)

Scanning electron micrograph observations of the olfactory mucosa from both unpigmented glass eel(GE)andpigmentedelvers(EL)of the European eel, Anguilla anguilla (L.), revealed the presence of various cell types; amongst these, the ciliated and microvillous ones are likely to possess a chcmosensory function. Recording of underwater electro-olfactograms (EOGs) showed that various amino acids (glycine, L-alanine, L-valine, L-leucine, L-asparagine, L-glutamine and L-methionine) are effective stimulants for the olfactory mucosa. Dose response curves of stimulus concentrations v. EOG amplitudesfit regression linesat both GE and EL stages. Leucine was more stimulatory at the GE than at the EL stage. The stimulatory effect of the other six amino acids tested was similar at both developmental stages. The possible role of olfactory sensitivity in animal behaviour at different developmental stages is discussed.