Vomeronasal Receptor Cells Research Articles

Morphological and histochemical changes in the regenerating vomeronasal epithelium.

Receptor cell degeneration and regeneration within the vomeronasal organ (VNO) of the rat was studied using both electron microscopy and histochemical methods. Electron microscopy was employed to examine the morphological changes along the surface of the sensory epithelium, and histochemical markers were used to monitor the changes in the epithelial cell layers. Transection of the vomeronasal nerves induced selective degeneration of the receptor cells, and within six days, a significant decrease in the number of receptor cells was observed. During the subsequent stage of receptor cell regeneration, cilia and bud-like structures characteristic of a developing sensory epithelium were seen. By day 15, thin microvilli covering the surface of the receptor cells reappeared in the sensory epithelium. The neural cell adhesion molecule (NCAM) and two vomeronasal system-specific lectins; 1) Bandeiraea simplicifolia lectin (BSL-I) and 2) Vicia villosa agglutinin (VVA) were used as the histochemical markers. NCAM immunoreactivity on the surface of the epithelium was observed to be decreased significantly six days after nerve transection, and was restored during receptor cell regeneration (day 15). The reactivity of the two lectins, BSL-I and VVA, was decreased slightly during degeneration, but was still detectable at the time of maximum receptor cell degeneration (day 6). Lectin reactivity was restored to control levels by day 15. These findings suggest that (1) NCAM is a useful marker for vomeronasal receptor cells and that the vomeronasal system-specific lectins may bind to both receptor and supporting cells and (2) degeneration of vomeronasal receptor cells occurs during the first week (day 6) following nerve transection and the receptor cell population begins to recover within 15 days. The morphological changes observed during receptor cell regeneration suggest that the stages of VNO receptor cell regeneration are similar to those observed during development.

The expressed localization of rat putative pheromone receptors

The localization of pheromone receptors in the rat vomeronasal epithelium was examined by light- and electron-microscopic immunocytochemical analysis, using affinity-purified polyclonal antibodies. The antibodies were raised against a synthetic oligopeptide corresponding to a partial sequence of the rat putative pheromone receptor (VN6). Positive immunoreactivity was observed on the luminal surface of the sensory epithelium, and was abolished when an excess of the antigen peptide was added to the primary reaction solution. On electron microscopy, the immunoreactivity for the VN6 peptide was localized at the dendritic knobs and microvilli of receptor cells, but not in those of the supporting cells. These results show the first evidence of cellular localization of putative pheromone receptors in rat vomeronasal receptor cells.

Activation of an anatomically distinct subpopulation of accessory olfactory bulb neurons by chemosensory stimulation

Chemosensory cues known as pheromones play a key role in rodent reproductive physiology and social interactions. Pheromone molecules are detected by receptor cells located in the vomeronasal organ and conveyed exclusively to the accessory olfactory bulb, and then to limbic and hypothalamic sites for integration with other factors modulating reproductive physiology. We report here that chemosensory cues from the female mouse selectively activate a subpopulation of cells located in the anterior part of the accessory olfactory bulb of the male mouse. Exposure of male mice to female-soiled bedding resulted in a massive induction of c-fos expression, which was primarily confined to neurons located in the anterior part of the accessory olfactory bulb and was eliminated by removal of the vomeronasal organ. Exposure of the male to soiled bedding from a different stain of male mice also elevated c-fos expression, but immunoreactive cells were more evenly distributed along the anterior–posterior axis of the accessory olfactory bulb. No treatment effects were observed in the main olfactory bulb. Previous studies have indicated that vomeronasal receptor neurons are divided into two populations based on location within the organ, site of termination in the accessory olfactory bulb, second messenger content and putative pheromone receptor expression. The present study suggests that the two populations of vomeronasal receptor neurons detect different chemosensory stimuli. Since male mouse- and female mouse-specific urinary substances modulate different aspects of male mouse behavior, the present results suggest that anatomically segregated populations of vomeronasal organ receptor cells modulate distinct behavioral patterns.

Recent Topics in Molecular Mechanisms of Olfaction and Taste.

G-protein coupled receptors (GCR) have been cloned from olfactory, vomeronasal and taste organs. Roles of these receptors in these organs are discussed. Olfactory and gustatory responses are induced via cAMP-dependent pathway, IP3-dependent pathway and second messenger-independent pathway. A single olfactory cell responds to various species of odorants, although a single olfactory cell has only one type of GCR. The responses of mammalian vomeronasal receptor cells to pheromones are induced via IP3. A single rat vomeronasal receptor cell responds only to one species of urine which contains pheromones. The receptor mechanisms of sweet, bitter and umami substances are discussed.

Replacement of receptor cells in the hamster vomeronasal epithelium after nerve transection.

Chemoreceptor cells in the vomeronasal and olfactory epithelium are replaced following experimentally induced degeneration. This study analyzes quantitatively the time course and degree of vomeronasal receptor cell replacement. Unilateral transection of the vomeronasal nerves in adult hamster was used to induce a retrograde degeneration of receptor cells in the vomeronasal organ. Histological measurement of both number of receptor cells and epithelial thickness were made for recovery times from 0 to 60 days. After nerve transection, there was a gradual degeneration of receptor cells, the number decreasing to 50% of control by day 2 and 16% by day 6. During days 7-15 maximum receptor cell replacement was observed. Cell number increased rapidly and reached a peak on day 15. At recovery times of 40-60 days, cell number returned to the control level. Epithelial thickness, however, decreased to 60-70% during the degeneration period (days 4-6) and did not return to control levels. After 40-60 days epithelial thickness remained at 70% of control. These results demonstrate that vomeronasal receptor cells are replaced following degeneration, but epithelial thickness does not return to control levels. These findings suggest that the number of replacement cells is not limited by the reduced thickness of the epithelium, and that recovery mechanisms may function to restore an optimum number of receptor cells.

Scanning electron microscopy and gramicidin patch clamp recordings of microvillous receptor neurons dissociated from the rat vomeronasal organ.

Vomeronasal organs from female rats were dissociated and isolated microvillous receptor neurons were studied. The isolated receptor neurons kept the typical bipolar shape which they have in situ as observed by scanning electron microscopy. We applied the perforated patch-clamp technique using the cation-selective ionophore gramicidin on freshly isolated and well differentiated receptor neurons. The mean resting potential was -58+/-14 mV (n=39). The contribution of the sodium pump current to the resting potential was demonstrated by lowering the K+ concentration in the bath or by application of 100 microM dihydro-ouabain. The input resistance was in the range of 1-6 GOmega and depolarizing current pulses of a few pA were sufficient to trigger overshooting action potentials. In voltage clamp conditions a fast transient sodium inward current and a sustained outward potassium current were activated by membrane depolarization. These observations indicate that freshly isolated vomeronasal receptor neurons of rats can be recorded, using gramicidin, with little modification of the intracellular content. Their electrophysiological properties are very similar to those observed in situ. Four out of eight female vomeronasal receptor cells were depolarized by diluted rat male urine.

Ultrastructural aspects of olfactory signaling.

The olfactory area of the nasal cavity is lined with olfactory receptor cell cilia that come in contact with incoming odor molecules. Ultrastructural immunocytochemical studies in rodents have shown that these cilia contain all the proteins necessary to transduce the odorous message into an electrical signal that can be transmitted to the brain. These signaling proteins include putative odor receptors, GTP binding proteins, type III adenylyl cyclase and cyclic nucleotide-gated channels. The rest of the cells, including dendrites and dendritic knobs, showed no discernible labeling with antibodies to these signaling proteins. Furthermore, freeze-fracture and freeze-etch studies have shown that the membrane morphology of olfactory cilia differs substantially from that of non-sensory cilia. Olfactory cilia have many more membrane particles. Transmembrane signaling proteins, such as odor receptors, adenylyl cyclase and cyclic nucleotide-gated channels, conceivably appear as membrane particles. Thus, the long-standing supposition that olfactory cilia are peculiarly adapted to deal with the reception and initial transduction of odorous messages has now been verified in terms of both ultrastructural morphology and cytochemistry. Emerging studies on vomeronasal receptor cell microvilli indicate that the same is true for this organ, even though the actual signaling components differ from those of the main olfactory system.

Identification of surface glycoconjugates in the olfactory system of turtle

Lectin binding histochemistry was performed on the olfactory system of Pseudemys scripta to investigate the distribution and density of defined carbohydrate terminals on the cell surface glycoproteins of the olfactory receptors and their terminals in the olfactory bulbs. The lectin staining patterns indicate that the receptor cells of the olfactory mucosa are characterized by glycoconjugates containing α-d-galactose and N-acetyl-d-glucosamine terminal residues. The vomeronasal receptor cells contain instead α-N-acetyl-d-galactosamine, N-acetyl-d-glucosamine and α-d-galactose residues. The results demonstrate that the vomeronasal receptor cells contain high density of α-N-acetyl-d-galactosamine sugar residues that are not expressed by receptor cells of the olfactory mucosa. The presence of specific glycoproteins, whose terminal sugars are detected by lectin binding, might be related to the chemoreception and transduction of the odorous message into a nervous signal or in the histogenesis of the olfactory system. In fact, the olfactory receptors are the only known neurons in the vertebrate nervous system that undergo a continual cycle of proliferation not only in developing animals but also in mature ones. Moreover the results show that BSA-I-B4, an α-d-galactosyl-specific isolectin, targets the terminal sugar residues in the ramified microglial cells.

Identification of surface glycoconjugates in the olfactory system of turtle

Lectin binding histochemistry was performed on the olfactory system of Pseudemys scripta to investigate the distribution and density of defined carbohydrate terminals on the cell surface glycoproteins of the olfactory receptors and their terminals in the olfactory bulbs. The lectin staining patterns indicate that the receptor cells of the olfactory mucosa are characterized by glycoconjugates containing α- d-galactose and N-acetyl- d-glucosamine terminal residues. The vomeronasal receptor cells contain instead α- N-acetyl- d-galactosamine, N-acetyl- d-glucosamine and α- d-galactose residues. The results demonstrate that the vomeronasal receptor cells contain high density of α- N-acetyl- d-galactosamine sugar residues that are not expressed by receptor cells of the olfactory mucosa. The presence of specific glycoproteins, whose terminal sugars are detected by lectin binding, might be related to the chemoreception and transduction of the odorous message into a nervous signal or in the histogenesis of the olfactory system. In fact, the olfactory receptors are the only known neurons in the vertebrate nervous system that undergo a continual cycle of proliferation not only in developing animals but also in mature ones. Moreover the results show that BSA-I-B 4, an α- d-galactosyl-specific isolectin, targets the terminal sugar residues in the ramified microglial cells.

Electrophysiological evidence for glutamate as a vomeronasal receptor cell neurotransmitter

Bipolar receptor cells in the vomeronasal organ send axonal projections to the accessory olfactory bulb where they synapse with mitral cell dendrites. Although the nature of the synapse is thought to be excitatory, the neurotransmitter(s) involved has not yet been identified. Electrophysiological recordings of single neurons in the mitral cell layer of the AOB in response to vomeronasal nerve stimulation were conducted to characterize the synaptic response and the underlying neurotransmitter substance. Extracellular activity was recorded in vivo (whole animal) and in vitro (AOB slice) from female rats. In vivo, the predominant response to stimulation of the VNO was excitation. In many instances in the whole animal preparation, the excitation was followed by an inhibitory response. Attempts to block the excitatory response by ejecting kynurenic acid in close proximity to the mitral cell being recorded were not successful. Since this failure may have been due to inability of the antagonist to reach its presumed site of action at the dendrite, further recordings were carried out in vitro. In the AOB slice preparation, the predominant response to stimulation of the VN nerve endings was excitation. Superfusion of the non-NMDA antagonist, CNQX, into the medium resulted in a reduction of the orthodromic excitation in 5 of 8 cells. The NMDA antagonist, AP-5, was found to blunt orthodromic excitation in 1 of 4 cells. These results suggest that the excitatory response evoked in mitral cells following stimulation of the VN nerve is mediated by glutamate.

Anatomy and forebrain projections of the olfactory and vomeronasal organs in axolotls (Ambystoma mexicanum).

We examined the anatomy of the nasal cavity and forebrain in the axolotl (Ambystoma mexicanum) to determine whether the olfactory and vomeronasal systems are present in this neotenic aquatic salamander. The current study was motivated by two considerations: (a) little is known of the anatomy of the vomeronasal system in aquatic vertebrates, and (b) the presence of both olfactory and vomeronasal systems in larval amphibians has broad implications for the evaluation of these systems in vertebrates. From cresyl-violet-stained sections of snouts we determined that the nasal cavity of axolotls is much like that of terrestrial salamanders. The main chamber of the nasal cavity contains an olfactory epithelium, which is confined to grooves between longitudinal ridges of connective tissue covered in a nonsensory epithelium which lacks goblet cells. Using transmission electron microscopy, we found morphologically distinct olfactory receptor cells: many receptor cells terminate in microvillar dendrites, and fewer terminate in motile cilia with the 9 + 2 microtubule array typical of vertebrate olfactory receptor cells. The ciliated and microvillar cells occur in clusters with little intermingling. Horseradish peroxidase labeling revealed that axons of the olfactory receptor cells terminate in large glomeruli in the main olfactory bulb at the rostral end of the telencephalon. Lateral to the main chamber of the nasal cavity is a diverticulum that is entirely lined with a vomeronasal epithelium containing basal cells, microvillar receptor cells, sustentacular cells that lack specialized processes on the apical surface, and large ciliated cells that may function to move fluid across the vomeronasal epithelium. Unlike the olfactory epithelium, the vomeronasal epithelium lacks Bowman's glands. Using horseradish peroxidase, we determined that the axons of the vomeronasal receptor cells project to the accessory olfactory bulb, a distinct structure dorsal and caudal to the main olfactory bulb. The presence of both olfactory and vomeronasal systems in axolotls and other neotenic salamanders implies that both systems are pleiomorphic in larval amphibians; we therefore suggest that the vomeronasal system may not have originated as an adaptation to terrestrial life.

Anatomy and Forebrain Projections of the Olfactory and Vomeronasal Organs in Axolotls <i>(Ambystoma mexicanum)</i> (Part 2 of 2)

We examined the anatomy of the nasal cavity and forebrain in the axolotl <i>(Ambystoma mexicanum) </i>to determine whether the olfactory and vomeronasal systems are present in this neotenic aquatic salamander. The current study was motivated by two considerations: (a) little is known of the anatomy of the vomeronasal system in aquatic vertebrates, and (b) the presence of both olfactory and vomeronasal systems in larval amphibians has broad implications for the evolution of these systems in vertebrates. From cresyl-violet-stained sections of snouts we determined that the nasal cavity of axolotls is much like that of terrestrial salamanders. The main chamber of the nasal cavity contains an olfactory epithelium, which is confined to grooves between longitudinal ridges of connective tissue covered in a nonsensory epithelium which lacks goblet cells. Using transmission electron microscopy, we found morphologically distinct olfactory receptor cells: many receptor cells terminate in microvillar dendrites, and fewer terminate in motile cilia with the 9 + 2 microtubule array typical of vertebrate olfactory receptor cells. The ciliated and microvillar cells occur in clusters with little intermingling. Horseradish peroxidase labeling revealed that axons of the olfactory receptor cells terminate in large glomeruli in the main olfactory bulb at the rostral end of the telencephalon. Lateral to the main chamber of the nasal cavity is a diverticulum that is entirely lined with a vomeronasal epithelium containing basal cells, microvillar receptor cells, sustentacular cells that lack specialized processes on the apical surface, and large ciliated cells that may function to move fluid across the vomeronasal epithelium. Unlike the olfactory epithelium, the vomeronasal epithelium lacks Bowman's glands. Using horseradish peroxidase, we determined that the axons of the vomeronasal receptor cells project to the accessory olfactory bulb, a distinct structure dorsal and caudal to the main olfactory bulb. The presence of both olfactory and vomeronasal systems in axolotls and other neotenic salamanders implies that both systems are plesiomorphic in larval amphibians; we therefore suggest that the vomeronasal system may not have originated as an adaptation to terrestrial life.

Voltage‐dependent Currents in Microvillar Receptor Cells of the Frog Vomeronasal Organ

Vomeronasal receptor cells are differentiated bipolar neurons with a long dendrite bearing numerous microvilli. Isolated cells (with a mean dendritic length of 65 microns) and cells in mucosal slices were studied using whole-cell and Nystatin-perforated patch-clamp recordings. At rest, the membrane potential was -61 +/- 13 mV (mean +/- SD; n = 61). Sixty-four per cent of the cells had a resting potential in the range of -60 to -86 mV, with almost no spontaneous action potential. The input resistance was in the G omega range and overshooting repetitive action potentials were elicited by injecting depolarizing current pulses in the range of 2-10 pA. Voltage-dependent currents were characterized under voltage-clamp conditions. A transient fast inward current activating near -45 mV was blocked by tetrodotoxin. In isolated cells, it was half-deactivated at a membrane potential near -75 mV. An outward K+ current was blocked by internal Cs+ ions or by external tetraethylammonium or Ba2+ ions. A calcium-activated voltage-dependent potassium current was blocked by external Cd2+ ions. A voltage-dependent Ca2+ current was observed in an iso-osmotic BaCl2 solution. Finally, a hyperpolarization-activated inward current was recorded. Voltage-dependent currents in these microvillar olfactory receptor neurons appear qualitatively similar to those already described in ciliated olfactory receptor cells located in the principal olfactory epithelium.

Odor Responses of the Vomeronasal System in Reeve's Turtle, &lt;i&gt;Geoclemys reevesii&lt;/i&gt;

The number of vomeronasal receptor cells and olfactory receptor cells were determined in several turtles and tortoises. Using semi-aquatic turtles with developed vomeronasal organs, neural responses to various odor stimuli were recorded as extracellular unitary spike responses of vomeronasal receptor cells, compound action potentials from vomeronasal nerve twigs, induced wave responses on the accessory olfactory bulb (AOB) surface and unitary responses of AOB neurons. The vomeronasal system in turtles responded to various volatile and non-volatile chemicals. These results yield insights concerning functions of the vomeronasal organ in semi-aquatic turtles.

Developmental changes in expression of a calcium-binding protein (spot 35-calbindin) in the Nervus terminalis and the vomeronasal and olfactory receptor cells.

The detailed localization of spot 35-calbindin and its ontogenic change were studied in Nervus terminalis, the vomeronasal organ and the olfactory epithelium of the rat by immunohistochemistry. At the embryonic days 12 and 13 (E 12-13), calbindin-immunoreactive cells were found in the outermost layer of the presumptive olfactory bulb and within the olfactory placode. At E 14 to the postnatal day 1 (P 1), intense calbindin-immunoreactivity was localized in ganglionated fiber bundles of Nervus terminalis coursing through the mesenchymal spaces on both sides of the nasal septum. Nervus terminalis decreased the immunoreactivity abruptly after P 1 and it showed no distinct immunoreactivity for calbindin at P 7 and thereafter. On the other hand, numerous receptor cells in the olfactory epithelium and the thicker vomeronasal epithelium exhibited weak to moderate immunoreactivity for calbindin at E 18-P 1. Their immunoreactivity decreased in intensity progressively after P 7 and no distinct immunoreactivity for calbindin was detected in most of the receptor cells, whereas moderate immunoreactivity was detected in most of the vomeronasal and olfactory nerves at P 28 and P 63.

Sensitivity and transduction mechanisms of responses to general odorants in turtle vomeronasal system.

(a) The responses of the vomeronasal organ to general odorants in the turtle, Geoclemys reevesii, were measured by recording the accessory olfactory bulbar responses. The threshold concentrations of the vomeronasal responses to various odorants were similar to those in main olfactory bulbar responses, indicating that vomeronasal cells lacking cilia and olfactory cells having many cilia have similar sensitivities to general odorants. (b) The vomeronasal epithelium was perfused with 100 mM NaCl solution and the salt-free solution and the effects of NaCl on the vomeronasal responses to various odorants were examined. There was no essential difference between the concentration-response curves for n-amyl acetate and menthone dissolved in 100 mM NaCl solution and those dissolved in the salt-free solution in the whole concentration range examined. The ratios of the magnitudes of vomeronasal responses in the salt-free solution to those in 100 mM NaCl solution were between 1.01 and 1.10 for seven odorants tested. (c) The magnitudes of responses to the odorants were unchanged by changes in NaCl concentrations. The replacement of Na+ with organic cations such as choline+, Bis-Tris propane2+, and N-acetyl-D-glucosamine+ did not affect the magnitudes of the responses to the odorants. The Na channel blocker amiloride also did not affect the responses. (d) The vomeronasal responses were practically unchanged by changes in CaCl2 concentration. The Ca channel blockers diltiazem and verapamil did not affect the responses. (e) The replacement of Cl- with SO4(2-) did not affect the magnitudes of the vomeronasal responses. (f) The present results suggest that ion transport across the apical membranes of vomeronasal receptor cells does not contribute to the responses to odorants in the turtle.

Cellular expression of H and B antigens in the rat olfactory system during development.

Developmental expression of H and B antigens in the rat olfactory system was studied from the embryonic day 14 up to the postnatal day 30. The H antigen was detected in the olfactory and vomeronasal epithelia as early as fetal day 14, whereas the B antigen first appeared 2 days later. The anti-H reagent reacted strongly with sensory receptors and weakly with supporting cells in both epithelia, whereas the anti-B reagent was specific for olfactory receptors. In the main olfactory epithelium, the H antigen was expressed from fetal day 19 by most of the receptor cells, whereas the B determinant was expressed from fetal day 16 to postnatal day 3 by only a few neuroreceptors mostly located near the epithelial surface. After the postnatal day 3, B positive neurons increased in number from the periphery toward the deeper mucosal layers and they were distributed over 3/4 of the epithelial thickness in 15- and 30-day-old rats. In the main olfactory bulb, a widespread glomerular B staining with variable binding intensity between adjacent glomeruli was already observed at birth. The vomeronasal receptor cells and their axon terminals in the accessory olfactory bulb exhibited a comparable developmental expression of the B antigen. Results suggest that the B antigen could be regarded as a marker of neuronal maturation of both the olfactory and vomeronasal receptor cells; moreover, its first appearance in the receptor cells might be temporally related to the formation of synapses between receptor axons and deutoneurons in the bulb.

Monoclonal antibodies (2C5 and 4C9) against lactoseries carbohydrates identify subsets of olfactory and vomeronasal receptor cells and their axons in the rabbit

Monoclonal antibodies (MAbs) against lactoseries carbohydrates were used to study immunohistochemically the olfactory and vomeronasal receptor cells and their axons in the rabbit. MAb 2C5, which recognizes Galα1→3Galβ1→4G1cNAc→R structure, selectively labeled a subset of olfactory receptor cells and the majority of vomeronasal receptor cells. MAb 4C9, which reacts with fucosyl poly-N-acetyllactosamine, identified a subset of vomeronasal receptor cells. The above two MAbs also labeled the axons of these chemosensory receptor cells and thus revealed their axonal projection sites in the main and accessory olfactory bulbs.

Projections of two subclasses of vomeronasal nerve fibers to the accessory olfactory bulb in the rabbit

The organization of the projections of subclasses of vomeronasal nerve fibers to the accessory olfactory bulb was analysed using monoclonal antibodies generated against a homogenate of the rabbit olfactory bulb. Monoclonal antibody R2D5 labels all the somata of vomeronasal receptor cells in the vomeronasal organ as well as all their axons (vomeronasal nerve fibers). Another monoclonal antibody (R4B12), which has been shown to selectively bind and thus identify a subclass of olfactory nerve fibers, 7,18 also labels a subclass of vomeronasal nerve fibers. The R4B12-positive subclass of vomeronasal nerve fibers project to the glomeruli in the rostrolateral part of the accessory olfactory bulb. The third monoclonal antibody (R5A10) recognizes a complementary subclass of vomeronasal nerve fibers projecting to the glomeruli in the caudomedial part of the accessory bulb. In contrast to the clearly segregated terminations in the accessory bulb, the two subclasses of vomeronasal nerve fibers are intermingled with each other in the vomeronasal nerve bundles. Retrograde labeling of vomeronasal receptor cell somata following injection of horseradish peroxidase within the rostrolateral (R4B12-positive) part of the accessory bulb indicates that vomeronasal receptor cells of this subtype are widely distributed in the vomeronasal sensory epithelium. These results demonstrate the heterogeneity of vomeronasal receptor cells and the specificity of projections arising from subclasses of vomeronasal nerve fibers to the accessory olfactory bulb.

Ciliary-structure precursor bodies as stable constituents in the sensory cells of the vomero-nasal organ of reptiles and mammals.

The sensory cells of the vomero-nasal organ in reptiles and mammals do not develop cilia. In several species they contain centrioles together with cilium-structure precursor bodies measuring 400–700 A in diameter. These structures resemble axonemal precursor bodies which are known to occur in developing ciliated cells. They are enclosed in a fibrogranular matrix. The precursor bodies are resistant to pepsin digestion in Araldite sections. In Tupaia precursor bodies may join periodically in a row. In the vomero-nasal receptor cells the precursor bodies can be considered stabilized with a corresponding reduction of cilia. The periodically arranged precursor bodies could represent a special storage form.