Ciliated Receptor Cells Research Articles

Olfactory receptor OR52N2 for PGE2 in mediation of guppy courtship behaviors

Prostaglandins (PGs) are a type of physiologically active unsaturated fatty acids. As an important sex pheromone, PGs play a vital role in regulating the reproductive behaviors of species by mediating nerve and endocrine responses. In this study, guppy (Poecilia reticulate) was used as the model specie to detect the function of PGE2 in inducing the onset of courtship behaviors. Our results showed that adding PGE2 into the water environment could activate the courtship behavior of male guppy, indicating that the peripheral olfactory system mediated the PGE2 function. Thereafter, the open reading frame (ORF) of olfactory receptor or52n2 was cloned, which was 936 bp in length, coding 311 amino acids. As a typical G protein-coupled receptor, OR52N2 had a conservative seven α-helix transmembrane domains. To confirm the regulatory relationship between OR52N2 and PGE2, dual-luciferase reporter assay was employed to verify the activation of downstream CREB signaling pathways. Results showed that PGE2 significantly enhanced CRE promoter activity in or52n2 ORF transient transfected HEK-293 T cells. Finally, localization of or52n2 mRNA were observed in ciliated receptor cells of the olfactory epithelium using in situ hybridization. Our results provide a novel insight into sex pheromone signaling transduction in reproductive behavior.

Transcriptome Analysis Reveals Sexual Disparities between Olfactory and Immune Gene Expression in the Olfactory Epithelium of Megalobrama amblycephala.

The olfactory organ is an important chemoreceptor in vertebrates. However, the sexual disparities in gene expression patterns in the olfactory organ in fish remain unstudied. Here, we conducted a transcriptome analysis of the olfactory epithelium (OE) of male and female blunt snout bream (Megalobrama amblycephala) to identify the differences. The histological analysis showed that there were 22 leaf-like olfactory lamellaes on one side of the OE of the adult blunt snout bream. The sensory area of OE is enriched with ciliated receptor cells and microvilli receptor cells. The transcriptome analysis showed that only 10 out of 336 olfactory receptor genes (224 ORs, 5 V1Rs, 55 V2Rs, and 52 TAARs) exhibited significant expression differences between males and females, and most of the differentially expressed genes were related to the immune system. We also validated these results using qPCR: 10 OR genes and 6 immunity-related genes significantly differed between males and females. The FISH analysis results indicated that the ORs were mainly expressed at the edge of the olfactory lamellae. Collectively, our study reveals that gender is not an important factor influencing the expression of olfactory receptors, but the expression of immune genes varies greatly between the genders in blunt snout bream.

Microscopic structure of the olfactory mucosa of onespot barb, Puntius terio (Cyprinidae: Smiliogastrinae)

Light microscopy and scanning electron microscopy were used to portray the cellular constituents lining the olfactory epithelium of teri barb, Puntius terio (Hamilton, 1822) (Cyprinidae: Smiliogastrinae). The olfactory organ holded 16 pairs of lamellae emitted from central raphe, consummate an oviform rosette. The multilamellar olfactory rosette was distinctively placed on the ground of nasal cavity and differentiated by specialized sensory and non-sensory territory. Sensory epithelium covered apical part and linguiform process of lamella while rest part is disguised by non-sensory epithelium. The sensory epithelium had two specific forms: ciliated receptor cells and microvillous receptor cells categorized by staining magnitude, texture and surface morphology. In divergence, the nonsensory epithelium was made up of stratified epithelial cells with microridges, cluster of ciliated non-sensory cells and secretory mucous cells. Basal cells were buried in the mucosa, presumed to be the progenitor of sensory or other supporting cells. Functional implication of cellular components on the olfactory lining was argued with feeding habits and behaviour of fish interested.

Histoanatomy and surface ultrastructure of the olfactory organ of the freshwater tank goby, Glossogobius giuris (Hamilton, 1822)

Abstract Characteristic features of histology and fine morphology of the olfactory organ in the tank goby, Glossogobius giuris (Perciformes, Gobiidae, Gobiinae), were investigated with light and scanning electron microscopy. The olfactory cavity contained single lamellae that were exposed to the aquatic environment by small anterior and posterior nostrils. Typical olfactory rosettes were not observed. Histologically, each lamella consisted of two layers of epithelium; wrapping the central core that was composed of connective tissue stroma with nerve fibers and blood capillaries. The mucosal lining of lamella was merged with sensory and non-sensory olfactory cells, identified on the basis of structural characters, surface specializations, and staining features. The principal sensory elements were ciliated receptor cells that were characterized by apical dendritic processes expanded from cell soma and microvillous receptor cells equipped with multiple tiny dendrons on the mucosal surface. The bead-like appearance of several labyrinth cells, mucous cells with secreted mucin, scattered lymphatic cells, stratified epithelial cells bearing microfolds, and condensed ciliated supporting cells were observed in the non-sensory epithelia. Undifferentiated basal cells were embedded in the deeper zone of the epithelium above the basement membrane. The cellular organization of the olfactory lining was interpreted with chemoreception of the fish concerned.

Ultrastructure and Development of the Olfactory Organ in Indigenous Pelophylax Ridibundus (Amphibia, Rana)

Two olfactory placodes were formed in early embryonic stages. The olfactory epithelia contain receptor, supporting and basal cells. Receptor cells are represented by elongated ciliated cells or microvillated cells, most of the supporting cells are ciliated and some of them are secretory cells. The olfactory placode developed into a principal cavity that differentiated into three chambers as ciliated supporting cells, secretory supporting cells and abundance of ciliated receptor cells and microvillated cells. We observed a tiny projections of small secretory supporting cells of the principle cavity, arranged in row, known as Bowman’s glands to detect odorants in the air, together with the surrounding supporting cells are presumply responsible for mucus-coating the epithelium of the principle cavity.

Histology and surface morphology of the olfactory epithelium in the freshwater teleost Clupisoma garua (Hamilton, 1822)

Abstract The anatomical structure of the olfactory organ and the organization of various cells lining the olfactory mucosa of Clupisoma garua (Siluriformes; Schilbeidae) were investigated with light and scanning electron microscopy. The olfactory organ was composed of numerous lamellae of various sizes, radiating outward from both sides of the narrow midline raphe, forming an elongated rosette. Each lamella consisted of the olfactory epithelium and a central lamellar space, the central core. The epithelium covering the surface of the rosette folds was differentiated into zones of sensory and indifferent epithelia. The sensory part of epithelium was characterized by three types of morphologically distinct receptor neurons: ciliated receptor cells, microvillous receptor cells, and rod receptor cells for receiving olfactory sensation from the aquatic environment. The indifferent epithelium comprising a large surface area of the lamella, was covered with compact non-sensory cilia. The non-sensory epithelium contained stratified epithelial cells with microridges, mucin secreting mucous cells, labyrinth cells, and basal cells, which were arranged in a layer at the base of the epithelium. Various cells on the olfactory epithelium were correlated with the functional significance of the fish concerned.

Histochemical and ultrastructural analyses of the lubrication systems in the olfactory organs of soft-shelled turtle.

In general, the nasal cavity of turtles is divided into two chambers: the upper chamber, lined with the olfactory epithelium containing ciliated olfactory receptor cells, and the lower chamber, lined with the vomeronasal epithelium containing microvillous receptor cells. In the nasal cavity of soft-shelled turtles, however, differences between the upper and lower chamber epithelia are unclear due to the presence of ciliated receptor cells in both epithelia. In the olfactory organ of vertebrates, the surface of sensory epithelium is covered with secretory products of associated glands and supporting cells, playing important roles in the olfaction by dissolving odorants and transporting them to the olfactory receptors. Here, the associated glands and supporting cells in the olfactory organ of soft-shelled turtles were analyzed histochemically and ultrastructurally. The upper chamber epithelium possessed associated glands, constituted by cells containing serous secretory granules; whereas, the lower chamber epithelium did not. In the upper chamber epithelium, secretory granules filled the supranuclear region of supporting cells, while most of the granules were distributed near the free border of supporting cells in the lower chamber epithelium. The secretory granules in the supporting cells of both epithelia were seromucous, but alcian blue stained them differently from each other. In addition, distinct expression of carbohydrates was suggested by the differences in lectin binding. These data indicate the quantitative and qualitative differences in the secretory properties between the upper and lower chamber epithelia, suggesting their distinct roles in the olfaction.

Immunohistochemical analysis for G protein in the olfactory organs of soft-shelled turtle, Pelodiscus sinensis.

In turtles, the epithelia lining the upper and lower chambers of the nasal cavity project axons to the ventral and dorsal parts of the olfactory bulbs, respectively. In a semi-aquatic soft-shelled turtle, Pelodiscus sinensis, more than 1,000 odorant receptor genes have been found, but it is not known where they are expressed. In this study, we aimed to clarify the distribution of cells expressing these genes in the olfactory organs of soft-shelled turtles. Immunoreactions for the Gαolf, the α subunit of G protein coupled to the odorant receptors, were detected on the surface of epithelia lining both the upper and lower chambers of the nasal cavity. The receptor cells in the epithelium of both chambers possessed cilia on the tip of their dendrites, whereas microvillous, non-ciliated, receptor cells were not found. These data suggest that the odorant receptor genes are expressed by the ciliated receptor cells in the upper and lower chamber epithelia. Precise location of the vomeronasal epithelium is not known at present.

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.

Development of sensory organs and changes of behavior in larvae of the sutchi catfish, Pangasianodon hypophthalmus

Larvae of the sutchi catfish Pangasianodon hypophthalmus hatch with morphologically immature features, but sensory organs develop rapidly as the fish grow. By 1 day old, yolk-sac larvae showed notochord flexion, and by 2 days old larvae were observed to have consumed a large part of the yolk sac. At this stage, larvae had well-developed eyes, olfactory organs with ciliated receptor cells, inner ears with semicircular canals, and numerous taste buds, and they commenced ingestion of rotifers, Artemia nauplii, and artificial compound feed. Two-day-old larvae had many free neuromasts on the surface of the head and flanks and clearly showed rheotaxis. By 20 days old, free neuromasts in postflexion larvae had sunk under the skin. At this later stage, larvae swam against a water current and schooled along the side of the fish tank. Rapid development of sensory organs and notochord flexion would be an adaptation for survival in conditions of flowing water, as in the Mekong River. In this study, we show that development of the lateral line in the postflexion stage seems to be closely related to larval behavior, suggesting that these developments could be essential for sutchi catfish larvae survival.

Functional morphology of the olfactory organ of the tongue sole, Cynoglossus semilaevis

The morphology and structure of the olfactory organ of Cynoglossus semilaevis Gunther are described. The oval olfactory sacs on both sides differ in size and in the number of lamellae, with those on the abocular side having smaller sacs and fewer lamellae than those on the ocular side. On the ocular side, the average ratio of sac length to eye diameter is 2.1 (i.e.>1) with an average of 91 lamellae, while on the abocular side, the values were 1.7 (i.e.>1) and 69, respectively. In addition, the surface morphology varies in different parts of the lamella. The frontal part, near the anterior nostril, is a non-sensory margin with cilia-free epidermal cells. Within this is an internal ciliated sensory area, which is intercalated with ciliated receptor cells and a few ciliated non-sensory cells. Additionally, some dense ciliated non-sensory cells make up a non-sensory area, which also contains cilia-free epidermal cells distributed in patches. In the rear of the olfactory sac near the posterior nostril, the lamellae differ in morphology from those of the frontal olfactory sac but are similar in having few ciliated receptor cells. In other words, the surface of the lamellae in the rear part of the olfactory sac is mainly non-sensory. At present, four types of lamellae (I, II, III and IV) have been recognized in relation to the pattern of the sensory epithelium. In this study, the frontal and rear lamellae resembled types I and IV, respectively, but are referred to as types I′ and IV′ because they are slightly less developed. Data on the ratio of length of lamellae to eye diameter, number of lamellae and the type of surface pattern of the lamellae show that the development of the olfactory system of C. semilaevis facilitates prey capture.

Development of the nasal olfactory organs in the larvae, settlement-stages and some adults of 14 species of Caribbean reef fishes (Labridae, Scaridae, Pomacentridae)

Larval fishes likely use a variety of settlement cues to locate and navigate toward the habitats they will inhabit as juveniles. Information about the morphology and state of development of the sensory organs of larval stages of fishes provides insight into their capabilities at the time of settlement. The peripheral olfactory organ of wild-caught late-stage larvae and early juveniles and some adults of 14 species of the Caribbean reef fishes wrasses (Labridae), parrot fishes (Scaridae) and damselfish (Pomacentridae) were examined using scanning electron microscopy and compared in terms of settlement specificity. Ages in days after hatching and days post-settlement were determined from the otoliths. Morphology of the nares and the olfactory epithelium are described for these species by stage. The separation of the anterior and posterior nares occurred before settlement in the labrids but in some specimens of scarids this separation was not complete by the time of settlement. Densities of ciliated and microvillous receptor cells and non-sensory ciliated epithelial cells were calculated. Densities of ciliated receptor cells ranged from 0.389 μm−2 in a specimen of Thallasoma bifasciatum to 0.0057 μm−2 in Bodianus rufus and of microvillous receptor cells from 0.038 μm−2 in a Clepticus parrae juvenile to 0.266 μm−2 in a juvenile Doratonotus megalepis. Densities of non-sensory cilia, also associated with high olfactory ability, were also high. The olfactory organ in wrasses is well developed prior to settlement and is comparable to that of adult fishes. The possible role of olfaction in larval schooling, reef cue detection and orientation toward habitat at settlement is discussed.

Olfactory metamorphosis in the Coastal Giant Salamander (Dicamptodon tenebrosus)

This study examined the gross morphology and ultrastructure of the olfactory organ of larvae, neotenic adults, and terrestrial adults of the Coastal Giant Salamander (Dicamptodon tenebrosus). The olfactory organ of all aquatic animals (larvae and neotenes) is similar in structure, forming a tube extending from the external naris to the choana. A nonsensory vestibule leads into the main olfactory cavity. The epithelium of the main olfactory cavity is thrown into a series of transverse valleys and ridges, with at least six dorsal and nine ventral valleys lined with olfactory epithelium, and separated by ridges of respiratory epithelium. The ridges enlarge with growth, forming large flaps extending into the lumen in neotenes. The vomeronasal organ is a diverticulum off the ventrolateral side of the main olfactory cavity. In terrestrial animals, by contrast, the vestibule has been lost. The main olfactory cavity has become much broader and dorsoventrally compressed. The prominent transverse ridges are lost, although small diagonal ridges of respiratory epithelium are found in the lateral region of the ventral olfactory epithelium. The posterior and posteromedial wall of the main olfactory cavity is composed of respiratory epithelium, in contrast to the olfactory epithelium found here in aquatic forms. The vomeronasal organ remains similar to that in large larvae, but is now connected to the mouth by a groove that extends back through the choana onto the palate. Bowman's glands are present in the main olfactory cavity at all stages, but are most abundant and best developed in terrestrial adults. They are lacking in the lateral olfactory epithelium of the main olfactory cavity. At the ultrastructural level, in aquatic animals receptor cells of the main olfactory cavity can have cilia, short microvilli, a mix of the two, or long microvilli. Supporting cells are of two types: secretory supporting cells with small, electron-dense secretory granules, and ciliated supporting cells. Receptor cells of the vomeronasal organ are exclusively microvillar, but supporting cells are secretory or ciliated, as in the main olfactory cavity. After metamorphosis two distinct types of sensory epithelium occur in the main olfactory cavity. The predominant epithelium, covering most of the roof and the medial part of the floor, is characterized by supporting cells with large, electron-lucent vesicles. The epithelium on the lateral floor of the main olfactory cavity, by contrast, resembles that of aquatic animals. Both types have both microvillar and ciliated receptor cells. No important changes are noted in cell types of the vomeronasal organ after metamorphosis. A literature survey suggests that some features of the metamorphic changes described here are characteristic of all salamanders, while others appear unique to D. tenebrosus.

Morphoecology in larval fin-fish: a new candidate species for aquaculture, Diplodus puntazzo (Sparidae)

This study was aimed to acquire information ontrophic behavior of Diplodus puntazzolarvae and juveniles, by studing theontogenetic sensory development, except vision.D. puntazzo specimens were observed usinga scanning electron (n = 67) and a lightmicroscope (n = 7). The results concerned fourontogenetical stages of sharpsnout seabream:larval, post-larval, transitional, and juvenilestages. The yolk-sac larval stage was notdetected as the smallest larvae at our disposal(3.1 mm TL; 2nd day from hatching) showedno external appearance of the yolk. During thelarval stage (3.1–4.7 mm TL), sharpsnoutseabream is equipped with free neuromasts andolfactory ciliated receptor cells. In thepost-larval stage (5–28.6 mm TL), mechano- andchemo-reception is implemented: the inner andouter taste buds differentiation, the nasalformation, the lateral line system canalizationoccur. The precocious differentiation ofchemo-receptors makes post-larvae particularlysensitive to the organoleptic properties ofadministered preys. D. puntazzo, at theend of this phase, could be considered ajuvenile (complete squamation is acquired),except for the mouth and pharyngeal teeth.During the subsequent phase (`transitional'),in fact, eight chisel-type and two lateralseries of molar-like teeth progressivelysubstituted the conical ones on each jaw, andthree different types of teeth on the upper andlower pharynx differentiated. So, the juvenilephase is reached in individuals longer than58 mm TL.

Ultrastructure of the olfactory organ in the clawed frog, Xenopus laevis, during larval development and metamorphosis.

Development of the olfactory epithelia of the African clawed frog, Xenopus laevis, was studied by scanning and transmission electron microscopy. Stages examined ranged from hatching through the end of metamorphosis. The larval olfactory organ consists of two chambers, the principal cavity and the vomeronasal organ (VNO). A third sensory chamber, the middle cavity, arises during metamorphosis. In larvae, the principal cavity is exposed to water-borne odorants, but after metamorphosis it is exposed to airborne odorants. The middle cavity and the VNO are always exposed to waterborne odorants. Electron microscopy reveals that in larvae, principal cavity receptor cells are of two types, ciliated and microvillar. Principal cavity supporting cells are also of two types, ciliated and secretory (with small, electron-lucent granules). After metamorphosis, the principal cavity contains only ciliated receptor cells and secretory supporting cells, and the cilia on the receptor cells are longer than in larvae. Supporting cell secretory granules are now large and electron-dense. In contrast, the middle cavity epithelium contains the same cell types seen in the larval principal cavity. The VNO has microvillar receptor cells and ciliated supporting cells throughout life. The cellular process by which the principal cavity epithelium changes during metamorphosis is not entirely clear. Morphological evidence from this study suggests that both microvillar and ciliated receptor cells die, to be replaced by newly generated cells. In addition, ciliated supporting cells also appear to die, whereas there is evidence that secretory supporting cells transdifferentiate into the adult type. In summary, significant developmental additions and neural plasticity are involved in remodeling the olfactory epithelium in Xenopus at metamorphosis.

The Lateral Line System of Hagfishes (Craniata: Myxinoidea)

AbstractThe morphology of the peripheral lateral line system in Eptatretus stoutiiis described using a combination of electron microscopical, histological and immunocytochemical techniques. The epidermis and cranial nerves of Myxine glutinosawere also examined for evidence of a lateral line system. Together with results previously published by other researchers, we conclude that most or all eptatretid hagfish possess a lateral line system composed of shallow trenches, or grooves, lined with a single class of flask‐shaped receptive cells. No species of myxinid hagfish has been shown to possess any component of this system. Three groups of lateral line grooves are present in eptatretids: preoptic, dorsal postoptic, and ventral postoptic groups. The preoptic grooves are innervated by a single pair of ganglionated cranial nerves and the two postoptic series of grooves are innervated by a pair of cranial nerves which each possess two ganglia, possibly as a result of fusion of two pairs of ganglionated nerves. Morphometric analysis indicates that these grooves continue to grow throughout life and that the variability in the distribution of grooves between animals may result from developmental instability in lateral line ontogeny. The morphology of the receptive organs is compared to neuromasts of the vertebrate lateral line system and ciliated receptor cells of other chordates. The morphology of hagfish lateral line receptors may represent the primitive condition for craniate lateral line organs, or more likely, they are highly derived as a result of regressive evolution. © 1997 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd.

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.

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.

Ciliated olfactory receptor neurons in goldfish (Carassius auratus) partially survive nerve axotomy, rapidly regenerate and respond to amino acids

Electro-olfactogram (EOG) recordings in response to amino acid stimulation were made from both control and experimental olfactory mucosae following unilateral axotomy. The recorded EOG amplitudes, amino acid stimulus relative effectiveness and dose-response relations for control and experimental mucosae were comparable in all pre- and postoperative recordings. Semi-thin investigations of olfactory mucosae showed degeneration of olfactory receptors but indicated that intact receptors were also present. SEM of olfactory mucosae revealed that ciliated receptor cells were present in both axotomized and control sides on postoperative days, whereas microvillous receptors completely degenerated and did not regenerate until 7 weeks post axotomy. The present findings along with previous behavioral observations suggest at least three possible sources of the EOGs recorded from the experimental olfactory mucosae following olfactory nerve transection: (1) young olfactory receptor neurons whose axons had not yet reached the region of the transected olfactory nerve; (2) newly-emerged olfactory receptor neurons; and (3) olfactory receptor neurons that had not degenerated.

Scanning and Transmission Electron Microscopical Observations on the Larvae of Priapulus caudatus (Priapulida)

Abstract Scanning electron microscopical studies revealed four distinct morphological larva‐types (not instars) of Priapulus caudatus whose lorica‐length measured 82–860 μm. The smallest of the larvae are round to oval, have 20 longitudinal ridges, a series of transverse ridges, and have two pairs of laterally situated tubuli near the posterior limits. The second larva‐type is dorsoventrally compressed, has a single dorsal and single unsculptured ventral plate each with a prominent midridge near the anterior limits, three infolded lateral plates with a pair of tubuli near the posterior limits. The third and fourth larva‐types remain dorsoventrally flattened; the third larva‐type has less pronounced sculpturing than the fourth larva‐type and is smaller; two pairs of tubuli are situated as in the previous stage. The number and arrangement of scalids on the introvert and pharyngeal teeth differ according to each of the four larva‐types and are described. The ultrastructure of all organ systems is described. All scalids are sensilla equipped with ciliated receptor cells. The cuticle is similar to the cuticle in the adult and differs fundamentally from the cuticle of larval Halicryptus. The trunk is richly supplied with sensory structures. Trunk tubuli contain secretory cells. Posteriorly, a gland complex was found which presumably is the precursor of the equivalent gland in postlarvae and adults. The implications of the first larva‐type's structural similarity to the larva of Tubiluchus are discussed.