A partially purified preparation of isolated chemosensory cilia from the olfactory epithelium of the bullfrog, Rana catesbeiana

Cilia at the tips of dendritic processes of olfactory receptor cells are the sites of initial recognition and transduction events in olfactory reception. We have detached cilia from the olfactory epithelium of the bullfrog, Rana catesbeiana, via a calcium shock and partially purified them in high yield (226 +/- 19 micrograms protein/frog, n = 14) by sucrose gradient centrifugation. The cilia appear to undergo osmotic lysis during the isolation procedure, forming isolated axonemal structures and ciliary plasma membrane vesicles with diameters of 100-500 nm and an internal volume of 2.3 +/- 0.5 microliter/mg protein. PAGE in SDS reveals approximately 30 protein bands, among which cytoskeletal components, such as tubulin and actin, are readily identifiable by immunoblotting. Approximately 15 glycoprotein bands reactive with concanavalin A are discernible with major glycopeptides at apparent molecular weights of 56-65, 95, and 116 kDa. In contrast to olfactory cilia, respiratory cilia, isolated from the palate of the frog, do not contain the prominent glycopeptides observed for olfactory cilia. The 56-65 kDa glycopeptide region reacts with antiserum against chick kidney, Na+/K+-ATPase, and contains the beta subunit of this enzyme. In addition, we have identified the alpha and beta subunits of a guanine nucleotide-binding protein (G-protein) in the olfactory cilia preparation. This preparation of isolated olfactory cilia from Rana catesbeiana represents a readily accessible model system for studies of initial events in chemosensory recognition and signal transduction in the olfactory system.

Ultrastructure of aesthetasc innervation and external morphology of the lateral antennule setae of the spiny lobster Panulirus interruptus (Randall)

Six types of setae and one type of cuticular depression were examined on the lateral antennule of the spiny lobster Panulirus interruptus using scanning electron microscopy. The organization and ultrastructure of the innervation of the most numerous setal type, the aesthetasc, were investigated using light- and transmission electron microscopy. Each aesthetasc is innervated by approximately 300 bipolar neurons whose sensory dendrites penetrate the hair and extend toward the tip, and whose axons project towards the central nervous system. The neuronal somata and two types of glia form a cluster within the antennular lumen. The inner sheath-cell somata encircle the dendritic tract distal to the sensory somata. These cells appear to extend distal processes which wrap the dendritic tract to the base of the aesthetasc. Elongate outer sheath cells are interposed between the glia-wrapped dendritic tract and the hypodermis which underlies the antennule cuticle. A continuous investment of neural lamella separates the hypodermis, the entire cluster of somata, and sensillar nerve from the antennule lumen. The organization of the neuronal somata and their association with outer and inner sheath cells in this marine species appear similar to those of crustaceans from freshwater and terrestrial habitats.

CO2 sensitive receptors on labial palps of Rhodogastria moths (Lepidoptera: Arctiidae): physiology, fine structure and central projection

The tips of the labial palps of Rhodogastria possess a pit housing uniform sensilla, histologically characterized by wall-pores and receptor cells with lamellated outer dendrites. The receptor cell axons project to glomeruli in the deutocerebrum which are not innervated by antennal receptors. From their histology as well as from their central projection these sense organs are identical with palpal pit organs of other Lepidoptera (Lee et al. 1985; Kent et al. 1986; Lee and Altner 1986). Physiologically, the palp-pit receptors respond uniformly; they are most excitable by stimulation with carbon dioxide while they exhibit relatively moderate responses to various odorants. The responses to CO2 show a steep dose-response characteristic. In ambient atmosphere (i.e., ca. 0.03% CO2) the cells are in an excited condition already; the seeming 'spontaneous activity' exhibited in air is decreased if the preparation is kept under N2 or O2 or CO2-free air. There is hardly any adaptation of the responses to continuous or repeated stimulation. Perhaps CO2 sensitivity is correlated with sensilla characterized by both wall-pores and lamellated dendrites. Pilot tests indicate that CO2 perception might be widespread in the Lepidoptera, but the biological significance remains obscure.

Destruction and reorganization of the receptor membrane in labellar chemosensory cells of the blowfly. Long-lasting latent action of colchicine

Electron micrographs of sections of the labellar chemosensilla of the blowfly, Phormia regina, showed that treatment with sodium deoxycholate (DOC; 7.2 mM for 2 min) destroyed the distal processes of the receptors from up to 10 microns from the tip of the sensillum, but these processes regenerated almost completely within 0.5 h. However, when DOC treatment was preceded by colchicine treatment (25 mM for 2 min), greater than 10 h was required for complete regeneration. Sugar receptor responses supported these findings and disclosed a more detailed time course of regeneration after DOC treatment: without colchicine pretreatment, the destroyed distal process completely regenerated in 0.3-1.0 h, but with pretreatment, regeneration began at 3 h and reached the chemosensillar tip at 8 h at the earliest. Hardly any depression of the response was observed for 8 h after treatment with colchicine alone, but a transient depression was detected at 12 h. Based on these results, the role of microtubules in the maintenance of the receptor membrane is discussed.

Effect of various vagotomy procedures on the reaction to hypoxia of rabbit neuroepithelial bodies: modulation by intrapulmonary axon reflexes?

Recent neuroanatomical investigations revealed the intrapulmonary neuroepithelial bodies (NEB) to be innervated to a large extent by sensory nerve fibers, displaying peripheral nerve endings of afferent as well as efferent morphology and having their cell bodies in the nodose ganglion of the vagus nerve. Earlier studies also revealed that upon exposure to acute hypoxia NEB exhibit a distinct secretory response, including as well a decrease in the cytoplasmic fluorescence as an increased basal exocytosis and indicating the secretion of serotonin. In the present study, we have tried to establish whether or not this secretory behavior is neurally controlled by combining an exposure to hypoxia with various vagotomy procedures. After long-term (3 days) infranodose vagotomy, the ipsilateral NEB nerve endings have degenerated. The secretory response to hypoxia is modified: the cytoplasmic fluorescence intensifies, while the basal exocytosis remains unchanged. After short-term (1 hour) infranodose as well as long-term (3 days) supranodose vagotomy, the NEB nerve endings are still intact, though no longer connected to the central nervous system. In these circumstances, the hypoxic NEB secretory behavior is indistinguishable from that of intact NEB. From these experimental findings we conclude that the hypoxic NEB secretory response is neurally controlled, since it no longer occurs when the normal innervation has degenerated. This modulation is however not by CNS motor nerve impulses, but probably by intrapulmonary axon reflexes in sensory nerve fibers.

[Ultrastructure of the osphradium of Siphonaria grisea (Mollusca, Pulmonata)]

By means of scanning and transmissive electron microscopic methods osphradium of Siphonaria grisea has been studied. The osphradium of the animal is presented as a small torulus formed by supporting ciliated cells. Among them bodies of receptory cells are situated; they are of smaller size and decorated with a bundle of microvilli. Central processes of the receptory cells, penetrating through a thick layer of the connective tissue, reach the subepithelial neural trunk. Concentration of the neural cells in the periphery of the trunk is small, and in the central area no chemical synapses are revealed. The data presented demonstrate a primitive structure of the osphradial chemoreceptory organ in Siphonaria.

Carotid body hyperplasia in cystic fibrosis and cyanotic heart disease. A combined morphometric, ultrastructural, and biochemical study

A combined morphometric, ultrastructural, and biochemical study was done on carotid bodies (CBs) obtained at autopsy from 213 patients in a pediatric and young adult population. The objective was to determine whether this group had statistically significant differences in sudden infant death syndrome (SIDS, n = 38), cystic fibrosis (CF, n = 30) and cyanotic heart disease (CHD, n = 17), compared with an age-matched control population (n = 128). Average combined weights of CBs in CF and CHD were significantly greater than those of controls in most age intervals (Student t test, P less than 0.05), and computerized planimetry showed an increase in both total surface area and area of "functional" parenchyma. There was diminished chief cell argyrophilia in 72% of CF CBs, and in 8 cases studied ultrastructurally there was moderate to marked depletion of dense-core neurosecretory granules. Most CBs from patients with CHD showed intense cytoplasmic argyrophilia similar to that of controls. Quantitative analysis for tissue catecholamines showed that dopamine was present in greatest concentration in each group of patients but was significantly elevated in CHD. There were no significant differences in morphometry, ultrastructure, or catecholamine content of CBs from SIDS victims, compared with age-related controls. These data add further support to CBs having a chemoreceptor role in humans with compensatory hypertrophy and hyperplasia occurring in most patients with chronic hypoxia due to CF and CHD. There were no significant findings to indicate that CBs play a direct role in the etiopathogenesis of SIDS.

Early development of olfactory receptor cell axons

An electron microscope study was done on development of olfactory receptor cell axons in rat fetuses 13-17 days after conception (E13-E17). Initiation of axon outgrowth was first seen on E13. On E14, small bundles of olfactory axons, accompanied by epithelial cells, grow out of the epithelium and, by so doing, breach the basal lamina. Close examination of these epithelial cells from E14 fetuses has revealed that they can be grouped into two types, one containing a ribosome-rich, dense cytoplasm, the other containing fewer free ribosomes and a more lucent cytoplasm. The first of these types is present infrequently or not at all at later times in development. The fate of the migrating cells is not known. Another notable observation was the indentation of olfactory epithelium by blood vessels during the developmental stages studied. There is very close association between processes of vascular endothelium and cells of the olfactory epithelium, so close, in fact, that a basal lamina is frequently absent. It is possible that vascular endothelium plays a role in breakdown of basal lamina, thus enabling olfactory axons to breach this barrier as they leave the epithelium.

Quantification of ultrastructural symmetry at molluscan chemical synapses

Two criteria were developed to identify symmetrical synapses in the tentacle ganglion of the snail Achatina fulica. First, the concentration of electron lucent vesicles within 20 nm of one membrane had to be less than three times the concentration at the opposed membrane. Second, paramembranous densities had to be present in both cells, as unanimously judged by three independent observers. Nine synapses (27% of sample) satisfied both criteria. It is suggested that these synapses transmit chemically in two directions.

Dendritic membrane from insect olfactory hairs: isolation method and electron microscopic observations

Sensory hairs from antennae of male saturniid moths (Antheraea polyphemus) were separated while deep-frozen by shaking antennal branches with glass beads. The hairs were collected through their differential adhesion to the surface of a petri dish. The yield, determined by the length of the isolated hair fragments, was about 38% of the estimated total hair length per antenna. The dendritic membrane was separated from the hair fragments by centrifugation through Sephadex and further purified by ultracentrifugation in sucrose buffers. Transmission electron microscopy was used to monitor the steps of the hair and membrane isolation and to investigate the membrane pellet. Some membrane vesicles bound cationized ferritin, thus indicating a negatively charged cell surface coat. Negatively stained membrane vesicles exhibited a pattern of repetitive substructures irregularly distributed over the vesicle surface. The units had a diameter of about 3 nm and a maximal density of 30,000/micron2.

Sir Thomas Lewis redivivus: from pebbles in a quiet pond to autonomic storms

Images

[Ultrastructure of the surface of the osphradium of the anterior gilled mollusk Murex saxatilis L]

The Murex saxatilis L. (Mollusca, Prosobranchia) osphradium is of the most complex "ctenidial" type and is situated immediately behind the siphon that brings water to the mantel cavity. By means of scanning and transmissive electron microscopical investigation, three zones have been revealed on the surface of the osphradium petals: secretory, intermediate and receptory. The secretory zone occupies the lateral part of the petal and is formed with 1-2 layers of cells. The intermediate zone, as a narrow stria, is situated between the secretory and the receptory zones. Here, together with the secretory cells, the ciliary cells are present. The receptory zone occupies nearly the whole surface of the petal. It is much thicker and is formed of pseudostratified epithelium where 5-7 raws of nuclei can be counted. Besides the cell types mentioned, there are defined bipolar receptory cells in it. The apical surface of the receptory cells has up to 200 cilia, and fine peripheral processes--1-2 cilia. Presence of the complex receptory zone makes it possible to suggest certain differentiation of the stimuli already at the peripheral level of the sensory system.

Ultrastructure of carotid bodies in sudden infant death syndrome

Recent studies have implicated an abnormality in carotid body structure and function in the pathogenesis of sudden infant death syndrome (SIDS). In the present investigation, the light and electron microscopic findings in carotid bodies from ten victims of SIDS were compared with those in six control infants and five infants dying of congenital heart disease. The cross-sectional area of carotid body chemoreceptor cells and the frequency, distribution, and size of neurosecretory granules were assessed morphometrically. The area of carotid body occupied by chemoreceptor cells (the functional area) was comparable in SIDS victims, control infants, and infants with congenital heart disease. By electron microscopy, the carotid body chief cells from all groups contained numerous electron-dense neurosecretory granules. Distribution, frequency, and size of neurosecretory granules in SIDS victims and control infants did not differ significantly. Morphology of carotid bodies from SIDS victims was found to be normal. The presence of neurosecretory granules in chemoreceptor cells of SIDS victims suggests that the cellular mechanism of neurotransmitter synthesis and storage is not altered.

Fine structure and molting of aesthetasc sense organs on the antennules of the isopod, Asellus aquaticus (Crustacea)

In Asellus aquaticus certain distal antennular segments bear single sensilla referred to as aesthetascs. These show a proximal stem and a distal bulbous region. Depending on its position, each aesthetasc is innervated by either 50-60 or 70-80 bipolar sensory cells, the perikarya of which are situated within the pedunculus. Within the antennular segment the dendrites develop unbranched cilia (9 X 2 + 0 structure). The sensory cells are unusual in that mono- as well as biciliary dendrites are present within a single aesthetasc, the ratio of both types being correlated with the number of sensory cells. Cilia and receptor lymph cavity are enveloped by a set of 3-4 inner and 13-14 outer sheath cells, which terminate at the base of the sensillum, so that the delicate and poreless cuticle of the bulbous region encloses only outer segments within the receptor lymph fluid. A new molting type in arthropods is described in which the outer sheath cells alone build the new cuticle, whereas the inner sheath cells most probably have a protective function. A definition of aesthetascs is proposed based on fine-structural criteria. Functionally the sensilla are considered to be chemoreceptors. This assumption is confirmed by experiments with diluted vital dye as well as lanthanum showing that dissolved substances penetrate the poreless cuticle instantaneously.

Carotid-body-like tissue within the recurrent laryngeal nerve: an endoneural chemosensitive micro-organ?

Paraganglia associated with the ninth and tenth cranial nerves have been observed in several locations in the head and neck region. The most studied of these organs, both morphologically and functionally, is the carotid body, a chemoreceptor organ located in the carotid bifurcation. In the present study a microglomus (microparaganglion) composed of islands of carotid-body-like cells was found in the endoneural space of the recurrent laryngeal nerve of rats, 5 to 10 mm from the nerve entrance into the larynx. This microglomus was surrounded by bundles of myelinated and unmyelinated nerve fibers. Fenestrated blood vessels were observed between cells. The cells were characterized by their cytoplasmic membrane-bound granules and dense-core vesicles. Ultrastructurally, these cells seemed to be identical to carotid body chemoreceptor cells and thus to indicate that the cells of the microglomus store catecholamines. Nerve terminals impinging on the cells, classified as both afferent and efferent, were also identified. The recurrent laryngeal endoneural microglomus may have a chemosensitive function influencing the laryngeal physiologic reflex mechanisms.

Morphology, distribution, and specificity of olfactory receptor cells in salmonid fishes

Electrophysiological and anatomical investigations of the olfactory epithelium of three salmonid species have been coordinated. Different corridors in the olfactory rosettes were examined by recording of the electro-olfactogram (EOG) using two recording electrodes simultaneously against one common indifferent electrode. Biopsies comprising the two lamellae bounding each of the examined corridors were examined by scanning electron microscopy (SEM). The electrophysiological results confirm a higher relative density of bile salt-receptors in the peripheral parts of all the corridors, and a higher relative density of amino acid-receptors in central parts. The SEM micrographs show that ciliated receptor cells are more numerous than microvillous ones. The density of ciliated receptor cells increases towards the peripheral margin of each lamella. The density of microvillous receptor cells increases towards the central margin. The correspondence between the electrophysiological and the anatomical observations support the hypothesis that the ciliated receptor cells are those specific to bile salt-like substances, the microvillous those specific to amino acids.

Structural properties of bimodal chemo- and mechanosensitive setae on the pereiopod chelae of the crayfish, Austropotamobius torrentium

The setae on the inner edges of the pereiopod chelae of Austropotamobius torrentium contain eight receptor-cell endings. Two units are mechanosensitive, four react only to amino acids, to amines, or to pyridines. The remaining two units are most probably also chemoreceptors. All sensory cells possess long dendritic outer segments that extend to the tip of the seta, where a small pore is found. Structurally, two units differ from the other six by having (1) densely packed microtubules in their dendritic outer segments, (2) dense A-tubules with arms in their ciliary segments, (3) a well-developed ciliary rootlet in their dendritic inner segments, and (4) desmosomal junctions between the dendritic inner segment and the inner enveloping cell, which contains a scolopale. These features are probably general characteristics of crustacean mechanoreceptors. The mechanoreceptors respond only to strong mechanical stimuli. This corresponds to the structural features of the setae, which lack specialized socket structures. Deflection of the setae may lead to longitudinal stress to the dendrites; the latter seem to be attached proximally to the inner enveloping cell and distally to the cuticle. Thus, the mechanoreceptor structure suggests a function analogous to scolopidial receptors. The chemoreceptors are accessible to chemical stimuli via the subterminal pore. The walls of the setae, however, may be permeable as well. It seems probable that action potentials were recorded also from the dendrites of the sensory cells.

Surface morphology of olfactory receptors

The receptor cells of the olfactory system have cilia on their apical terminals. The receptor cells of the vomeronasal system lack cilia on their distal terminals, having microvilli in their place. Since both these systems have the capacity to detect airborne stimuli, it is apparent that ciliary structure per se is not necessary for the chemoreceptive function and that cilia on olfactory receptor cells may then serve a mechanical or structural role for supporting specialized chemosensitive membrane. The spread of conductance changes across this chemosensitive membrane to proximal spike generating regions requires electrotonic cytoplasmic continuity from the ciliary shaft to the axon hillock. We have demonstrated this continuity by showing that intra-axonally injected HRP can spread from the axon to the cell soma and from there to the interior of the ciliary shafts.

The carotid body chemoreceptor: an investigation in the mouse

The carotid body chemoreceptor has been investigated in the normal mouse and in the wobbler mutant. Electron microscopic studies show that the synaptic vesicle-containing nerve endings on type I cells are reduced in number in the mutant to 4.2% of the normal number. The function of the chemoreceptors was examined by recording ventilation and testing the response to different inspired gases and to the intra-arterial injection of cyanide. In addition recordings of chemoreceptor activity were made from the sinus nerve. No distinction could be drawn between the normal and the mutant mouse. No relationship was found between chemoreceptor activity and the respiratory cycle. If the synaptic vesicle-containing endings are afferent then only 4.2% of the normal number appear to be needed for normal function.

Morphological observations on superficial medullary CO2--chemosensitive areas

Physiological investigations have indicated that the ventrolateral surface of the medulla oblongata is involved in the chemical drive to respiration. In this investigation, light and electron microscopic investigations of the 3 chemosensitive regions reveal the following. (1) Evaginations of the ventral surface abut the overlying pia mater thereby delimiting discrete compartments; invaginations of the surface delimit wide cisternae lined with basement membrane. Neuronal elements with numerous synapses, were found scattered among astrocytic processes of the marginal glia in intermediate and caudal chemosensitive areas Microvasculature are conspicuously absent from the marginal glia. Intramedullary vessels are surrounded by perivascular spaces and the endothelium shows zonulae occludentes at cell junctions. (2) Horseradish peroxidase (HRP) applied to the ventral surface diffused throughout the interstitial and perivascular compartments, into synaptic clefts and neuronal soma. Diffusion of HRP into blood vessels was blocked at zonulae occludentes. Following intravenous injection of HRP, no reaction product was found outside cerebral vasculature in chemosensitive areas. (3) In spontaneously breathing cats, 2% procaine applied to the caudal chemosensitive area resulted in respiratory depression which began with the second breath. It is proposed, that substances which stimulate or depress respiration, when applied to the ventral medullary surface, produce their effects on superficial neurons located in the intermediate and caudal chemosensitive areas after diffusion through interstitial spaces.

[Mechanisms of the effect of substances in the cerebrospinal fluid from the central canal of the spinal cord on hemodynamics]

The electron microscopy revealed morphological structures of the central spinal channel's wall capable of mediating physiological responses to administration of physiologically active substances in the CSF. The supraependymal dendrite terminals, the inter- and subependymal dendrites as well as chemoreceptors of subsynaptic membranes of the neuropil's axo-dendritic synapses are able to perform the receptor functions. The physiologically active substances of CSF can penetrate into the spinal cord and reach the receptor structures through the interependymal junctions and long basal branches of the ependyma cells.

Freeze-fracture characteristics of insect gustatory and olfactory sensilla. I. A comparison with vertebrate olfactory receptor cells with special reference to ciliary components

Freeze-fracture data on antennal olfactory and labellar gustatory sensilla of the blowfly Calliphora vicina were compared with those of vertebrate olfactory organs. Insect antennal and vertebrate olfactory axons have similar diameters and show vesicular expansions; insect labellar axons are on average twice as thick and show no vesicular expansions. Vertebrate olfactory and insect labellar and antennal axons display similar intramembranous particle densities. Antennal axons show particle arrangements, resembling tight-junctions. The few extremely thick axons found in labella and antennae show particle arrangements resembling gap-junctions. In regions, proximal to the pores in the insect sensillar hairs, P-faces of olfactory and gustatory cilia show about 200 particles/microns2. The most proximal and distal portions of the sensory cilia, necklaces and regions in the vicinity of the hair pores respectively, were only encountered in antennal sensilla. P-faces of the ciliary membranes underneath these pores display 1,000-1,200 particles/microns2 in unbranched and branched cilia. These values agree with values found in vertebrate olfactory cilia. It is suggested that these high particle densities are related to entities involved in chemoreceptive activities. Accessory cell micropliae have P-face densities of 2,000-3,000 particles/microns2, values similar to those found in vertebrate supportive cell microvilli. The membranes of the accessory cells display septate-junctions in areas where these cells overlap themselves, each other and in places where they adhere to the exoskeleton or the basement membrane.

Paddle cilia (discocilia) in chemosensitive structures of the gastropod mollusk Pleurobranchaea californica

Scanning electron microscopy of various regions of the body of the marine gastropod Pleurobranchaea californica (McFarland) has revealed a characteristic cell type that bears cilia with dilated discoid-shaped tips. The tips of the cilia consist of an expansion of the ciliary membrane around a looped distal extension of the axoneme. These kinocilia have been observed in numerous other marine invertebrates and are generally referred to as paddle cilia (Tamarin et al. 1974) or discocilia (Heimler 1978). Although many functions have been proposed for paddle cilia, little empirical evidence supports any of the proposals. In Pleurobranchaea we have found that the distribution of this ciliated cell type corresponds exactly to areas of the body known from behavioral studies (Lee et al. 1974; Davis and Matera 1981) to mediate chemoreception. Transmission electron microscopy of the epithelium lining the rhinophores and tentacles of Pleurobranchaea revealed details of the ultrastructure of these ciliated cells and showed that they are primary receptors. These ciliated receptors lie in a yellow-brown pseudostratified columnar epithelium that superficially resembles the olfactory mucosa of vertebrates.

Fine structure of the vomeronasal neuroepithelium of bats: a comparative study

The vomeronasal neuroepithelium of the vampire bat, Desmodus rotundus, and the frugivorous bats, Carollia perspicillata and Artibeus jamaicensis, was examined at the light-microscopic and ultrastructural levels. The neuroepithelium of these species is basically similar in morphology to that of other mammals. However, hitherto unknown differences were noted in regard to the configuration of the apical poles of cells, in the occurrence of solitary cilia, dislocated sensory cells, brush cells, cell contacts and the occurrence and fine structure of basal cells. The morphology of the vomeronasal neuroepithelium of all three species is discussed from a comparative point of view in regard to chemoreception.

Chemoreception in gastropod molluscs: electron microscopy of putative receptor cells

Scanning and transmission electron microscopy of the external surface of the gastropod mollusc Pleurobranchaea californica has revealed a new exteroreceptor, characterized by dense cilia (ac.200/cell) that project from an intraepithelial soma and exhibit dilated, discoid-shaped tips. The exteroreceptor is found in high densities (up to 5000/mm2) in areas of the body determined by behavioral assay to be chemosensitive, but nowhere else, suggesting that it is a chemoreceptor.

The effect of postsynaptic deprivation on the presynaptic chief cell in the rat carotid body

After the surgical removal of the postsynaptic sensory sinus nerve, the presynaptic specializations in the chief cell of the rat carotid body chemoreceptor rapidly disappear. When the sinus nerve is allowed to regenerate, the presynaptic specializations reappear almost simultaneously with the re-establishment of apposition of the nerve to chief cells and the number of the synapses is restored to a normal range by the third week after deafferentation. This finding indicates that the maintenance of the presynaptic specializations in the chief cell depends on the persistence of the postsynaptic element, and further suggest the neurotrophic maintenance of the presynaptic specializations may be exerted by the postsynaptic sinus nerve. The sustentacular cells may play a role in governing the specificity of reinnervation by the sinus nerve.

Fine-structural characteristics of the antennal sensilla of Agrotis segetum (Insecta: Lepidoptera)

The turnip moth Agrotis segetum possesses seven different types of sensilla: four single-walled (SW), one double-walled (DW), one terminal-pore (TP), and one poreless sensilla (NP). The SW 1 and SW 2 sensilla have the same external appearance, being long and slender, but differ in the branching pattern of the sensory processes: unbranched and branched in SW 1 and SW 2, respectively. The SW 3 sensilla are shorter, sickle-shaped, and contain a large number of branches from the sensory processes. These three sensillar types are innervated by 2--3 sensory cells. The SW 4 sensilla are raisin-shaped and possess three profusely branched sensory processes. The DW sensilla are short and have apical slit-like pores. This sensillar type has 5--6 sensory processes. The TP sensilla possess five sensory processes, one of them terminates basally in a tubular body, the others in the apical part of the long cuticular bristle. The NP sensilla are stout and have apical conelike structures. Two of the sensory processes terminate in the apical part, the third proximally. The third sensory process has a lamellar pattern. The fine structure indicates the following functions: SW and DW sensilla: chemoreception; TP sensillum: chemoreception and mechanoreception; NP sensillum: thermoreception and hygroreception.

Sensory control of dauer larva formation in Caenorhabditis elegans

As a sensory response to starvation or overcrowding, Caenorhabditis elegans second-stage larvae may molt into a developmentally arrested state called the dauer larva. When environmental conditions become favorable for growth, dauer larvae mold and resume development. Some mutants unable to form dauer larvae are simultaneously affected in a number of sensory functions, including chemotaxis and mating. The behavior and sensory neuroanatomy of three such mutants, representing three distinct genetic loci, have been determined and compared with wild-type strain. Morphological abnormalities in afferent nerve endings were detected in each mutant. Both amphid and outer labial sensilla are affected in the mutant CB1377 (daf-6)X, while another mutant, CB1387 (daf-10)IV, is abnormal in amphidial cells and in the tips of the cephalic neurons. The most pleitropic mutant, CB1379 (che-3)I, exhibits gross abnormalities in the tips of virtually all anterior and posterior sensory neurons. The primary structural defect in CB1377 appears to be in the nonneuronal amphidial sheath cells. The disruption of neural organization in CB1377 is much greater in the adult than in the L2 stage. Of all the anterior sense organs examined, only the amphids are morphologically affected in all three mutants. Thus, one or more of the amphidial neurons may mediate the sensory signals for entry into the dauer larva stage in normal animals. Using temperature-sensitive mutants we determined that the same defects which block entry into the dauer stage also prevent recovery of dauer larvae.

[Chemoreceptor organs of the antennae and maxillary palps of fleas (Siphonaptera)]

Ultrastructure of chemoreceptor sensillae on antennae and maxillary palps of fleas of Ceratophyllus sciurorum is described. On antennae of fleas are the following types of sensillae: trichoid cuspidate and obtusate, fungoid, basiconical sensillae in olfactory fossae and on the surface of antennae. On maxillary palps there are trichoid cuspidate, basiconical and campaniform sensillae. A comparison was made of the composition and number of chemo- and mechanoreceptor sensillae in 14 species of fleas differing in the type of parasitism. It has been established that "nest" fleas have the greatest number of sensillae.

Cephalic sense organs and body pores of Xiphinema americanum (Nematoda: Dorylaimoidea)

The fine structure of the cephalic sense organs and body pores of the plant parasitic nematode Xiphinema americanum is described by transmission electron microscopy. All of the six inner labial, six outer labial, and four cephalic sense organs as well as the amphids have characteristics indicating chemosensitivity, but there are no clearly identifiable mechanosensitive units. Two pairs of simple internal sense organs, not associated with cuticle, also occur. Sensory dendrites all bear cilium-derived dendritic processes that contain axonemal doublets of microtubules. These doublets show radial and circumferential linkages characteristic of the ciliary necklace region of a cilium, although only an amorphous microtubule organizing center occurs in the usual place of a basal body.Both socket cell and sheath cell processes are associated with the cuticular sense organs. The cell body of the amphidial sheath cell is located well anterior to the central nervous system, before the level of the buccal dilator muscles.Body pores are associated with sensory units characteristic of chemosensitive organs. Hypodermal cells serve as their socket cells, whereas a separate sheath cell occurs in the body wall close to each pore.

Regulation of chemoreceptor sensitivity in the carotid body: the role of presynaptic sensory nerves

Several neural and vascular mechanisms regulate the sensitivity of carotid body chemoreceptors to hypoxia, hypercapnia, and acidosis. Factors that control blood flow and oxygen delivery in the carotid body along with those that augment or diminish catecholamine release from glomus cells can have major effects on chemoreceptor function. In addition, the sensory nerves themselves may participate in the regulation of chemoreceptor sensitivity. A portion of the carotid body's sensory nerves are presynaptic to glomus cells. In response to stimulation, the sensory nerve terminals exhibit ultrastructural changes that resemble changes associated with increased release of transmitter from motor nerves: 1) the number of small (synaptic) vesicles decreases; and 2) coated vesicles and coated regions of cisternal membrane increase in number during stimulation. If sensory nerves of the carotid body release a neurotransmitters, sensory nerve activity could influence glomus cell secretion of catecholamines or other substances tha modify chemoreceptor sensitivity. Such an effect could be produced in the carotid body by hypoxia and other conditions that stimulate the sensory nerves or it could result from antidromic activity evoked in the sensory nerves by primary afferent depolarization of their terminals in the CNS.

Single-pore sensilla of damselfly-larvae: representatives of phylogenetically old contact chemoreceptors?

The four single-pore sensilla on the maxillary palp of Agrion and Ischnura possess two bipolar sensory cells for A-sensilla and five for B-sensilla. Distally, their dendrites are enclosed by a dendritic sheath and a pore tube. The dendritic tips have access to the outside via the opening of the pore tube. The inner dendritic segments join the receptor cell bodies laterally. The receptor cells of each sensillum are enveloped by three sheath cells and three receptor lymph cavities. Receptor lymph cavity 1 and 3 are connected with the outside by the pore tube and a minute canal system in the cuticle, respectively. All three sheath cells show microvilluslike processes of the apical membrane. Moreover, all sheath cells contain two centrioles in tandem arrangement. The structure of the single-pore sensilla is compared with that of similar sensilla of other arthropods. Functional and phylogenetic aspects are discussed.

Ultrastructure of the antennal sensilla of aphids. II. Trichoid, chordotonal and campaniform sensilla

An electron microscopical study of aphid antennal sensilla has revealed two types of trichoid sensilla. Type I, innervated by a single neuron is mechanoreceptive; type II, innervated by three to five neurons is both mechanoreceptive and chemoreceptive with possibly a third function. Johnston's organ in the pedicel comprises a peripheral ring of scolopidia inserted into the joint with the flagellum; two non-peripheral groups of scolopidia lie in the lumen with attachment points in the wall of the third segment. The fine structure of a campaniform sensillum on the pedicel is described together with two homologous and previously unknown sense organs at the joint between the fifth and sixth antennal segments. An unusually placed scolopidium in the lumen of the sixth segment has also been found. The function of this scolopidium is unknown but Johnston's organ, the campaniform sensillum and joint receptors are suggested to act as antennal proprioceptors.

A scanning and transmission electron microscope study of the premetamorphic papillae: possible chemoreceptive organs in the oral cavity of an anuran tadpole (Rana japonica)

Premetamorphic papillae of an anuran tadpole (Rana japonica) were studied by scanning and transmission electron microscopy. Premetamorphic papillae of several shapes are seen in and around the oral cavities of tadpoles during late larval and early metamorphic stages. These papillae are composed of three parts: the apical cellular part, the underlying connective tissue core and the epithelial covering. In the apical cellular part, two populations of cells are observed: apical and basal cells. The apical cell has a slender cytoplasmic process whose apical surface is exposed in the oral cavity. The basal cell is located at the basal portion of the apical cellular part of the papilla without researching the oral cavity. A long solitary microvillus and a bunch of short microvilli are seen on the apical surface of each apical cell. The apical cells contain dense-cored vesicles of 100 nm diameter and make synaptic contacts at their basal membranes with terminals of nerve fibers. Possible chemoreceptive function of the premetamorphic papilla is discussed.

[Morphofunctional characteristics of the accessory structures of the cat lingual receptors]

By means of scanning electron microscopy detailed topographic map of the cat tongue was made. It was demonstrated that besides three types of chemoreceptor formations, the dorsal surface of the cat tongue possess the same amount of additional mechanoreceptor structures. By means of registration of afferent impulses, from the lingual nerve fibres at their adequate stimulation, it was possible to determine functional role of some of them.

Fine structure of sensory tubes on the antennule of Conchoecia spinirostris (Ostracoda, Crustacea). A new type of sensillum in crustaceans

In addition to setae, the first antennae of Conchoecia spinirostris also bear soft sensory tubes (female: 4 tubes + 1 seta; male: 2 tubes + 3 setae). These tubes were examined electron microscopically. Each tube is divided into 4 regions: the stem, the bulbous region, the main region, and the tip. A tube contains 40--60 multiciliated dendrites, some hypodermal cells, and nonneuronal cells, and it has a specialized cuticle. Each dendrite develops within the tube, on the terminal 5--8 micron of its inner dendritic segment, approx. 25 cilia in a 9 X 2 + 0 pattern, whose rootlets are absent or only poorly developed. Each cilium splits up into 9 ramifications which extend into the tip. These ramifications partly take a spirallike course and form a ring in the distal main part beneath the cuticle. Their membranes often dilate into spindleshaped swellings. In the center of the middle and distal parts of the main region approx. 7 dendrites without cilia are located, one of them reaches into the tip. The poreless cuticle is extremely delicate and electron lucid. In contrast to the cuticle of the setae it is elastic and soft. Special substructures are described. The tubes are completely covered by a filamentous surface coat. Because of the structure and the thin walled nature of the cuticle, permeability for dissolved substances is assumed. The ciliary ramifications are likely to represent the receptive apparatus. The sensory tubes are interpreted as chemoreceptors. They can best be compared with the chemoreceptors of certain crustaceans, but differ strongly from the types of sensilla found in insects.

APUD-type recepto-secretory cells in the chicken lung

The epithelium of the intrapulmonary airways of the chicken lung has been studied by fluorescence and electron microscopy. Numerous intensely yellow-fluorescent cells occur in the epithelium of the primary and secondary bronchi. The cell cytoplasm contains characteristic granular vesicles with an electron-dense central core. The vesicles react positively to chromaffin and argentaffin treatment, indicating that they are possible storage sites for amines. Synapse-like junctions occur between the granular cells and the intraepithelial nerve endings, filled with numerous mitochondria, suggesting that these granular cells may have a dual function as both receptor and endocrine cell.

[Ultrastructural studies of Haller's organ in the argasid tick, Argas tridentatus (Argasidae)]

Haller's organ in A. tridentatus consists of a capsule and an anterior group of sensilla. The capsule is the hollow in the cuticle on the dorsal surface of the first tarsus, where 4 pored hairs of olfactory sensilla are situated under the cover of the roof, formed by an anostomosis of the upper brunches of pleomorphs (capsule's bottom non-sensory cuticular outgrowths). The canal of the accessory ampullaceous sensillum opens in a capsule near the bottom. The anterior group of sensilla consists of two parts: proximal part, containing pored grooved and thin hairs, is homologous to the anterior grouf of ixodid ticks, and distal one which has no homologues in ixodids. Fine structure of all the sensilla in the mentioned parts of Haller's organ is described in detail.

Fine structural comparison of the antennal nerve in the homeotic mutant Antennapedia with the wild-type antennal and second leg nerves of Drosophila melanogaster

In D. melanogaster the cross-sectioned nerve of the leg-like antenna in the homeotic mutant Antennapedia was ultrastructurally compared with the nerves of the morphologically related second leg and the wild-type antenna. The nerves of the normal antenna and the second leg differ from one another in both the numbers and arrangement of axons. According to these criteria the nerve of the homeotic appendage was structurally identified as a leg nerve. Most of the antennal nerves studied showed a consistent grouping of axons in the profile. This suggests that the assemblage of the axons does not occur randomly, but in an ordered fashion.

Tormogen cell and receptor-lymph space in insect olfactory sensilla. Fine structure and histochemical properties in Calliphora

(1) The basiconic sensilla on the antennae of Calliphora resemble other insect epidermal sensilla; one or several bipolar sense cells are surrounded by three non-neural cells. (2) The apical cell membrane of the tormogen cell (one of the three accessory cells) forms microvilli coated internally with particles. (3) In the (extracellular) outer receptor-lymph space hyaluronic acid can be demonstrated histochemically. (4) Demonstration of non-specific alkaline phosphatase, Mg2+-activated ATPase, and the presence of mitochondria in the apical part of the tormogen cell suggest active transport processes through these cells into the outer receptor-lymph space.

The ultrastructure of an olfactory sensillum on the maxillary palps of locusta migratoria (L.)

The olfactory sensilla on the maxillary palp tip of Locusta migratoria (L.) resemble the surrounding contact chemoreceptors in general morphology. The perforated peg has a thicker wall than is commonly found in olfactory sensilla. The form and position of the sensilla are considered in relation of the olfactory function. The fine structure of the dendrites is discussed in relation to that described in other olfactory sensilla.