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At least 685 records · Page 38Linked to original sources
PubMed2001

Neuroepithelial bodies in mammalian lung express functional serotonin type 3 receptor.

Serotonin (5-HT) type 3 receptor (5-HT(3)-R) is a ligand-gated ion channel found primarily in the central and peripheral nervous system. We report expression and functional characterization of 5-HT(3)-R in pulmonary neuroepithelial body (NEB) cells. Using nonisotopic in situ hybridization, we demonstrate expression of 5-HT(3)-R mRNA in NEB cells in the lungs of different mammals (hamster, rabbit, mouse, and human). Dual immunocytochemistry (for 5-HT and 5-HT(3)-R) and confocal microscopy localized 5-HT(3)-R on NEB cell plasma membrane from rabbit. The electrophysiological characteristics of 5-HT(3)-R in NEB cells were studied in fresh slices of neonatal hamster lung using the whole cell patch-clamp technique. Application of the 5-HT (5-150 microM) and 5-HT(3)-R agonist 2-methyl-5-HT (5-150 microM) induced inward currents in a concentration-dependent manner. The 5-HT-induced current was blocked (76.5 +/- 5.9%) by the specific 5-HT(3)-R antagonist ICS-205-930 (50 microM), whereas katanserin and p-4-iodo-N-(2-[4-(methoxyphenyl)-1-piperazinyl]ethyl)-N-2-pyridinylbenzamide had minimal effects. Forskolin had no effect on desensitization and amplitude of the 5-HT-induced current. The reduction of Ca(2+) and Mg(2+) in the extracellular solution enhanced the amplitude of the 5-HT-induced current because of slower desensitization. Our studies suggest that 5-HT(3)-R in NEB cells may function as an autoreceptor and may potentially be involved in modulation of hypoxia signaling.

Aminopyridines↗
PubMedDate not supplied

[Perception of chemical and temperature stimuli by the ampullae of Lorenzini in in skates].

Recording impulse activity in single nervous fibers, studies have been made on the effect of chemical and thermal stimuli on the activity of Lorenzini ampullae in the rays Dasyatis pastinaca and Raja clavata. Application of the diluted sea water to the opening of ampullary canal increases the discharge rate of the receptors resulting into subsequent adaptation, whereas the increase in water salinity causes opposite changes. Threshold changes in the salinity of sea water amount 1--2%. Thermal transient in the sea water at the vicinity of the opening of ampullary canal did not affect the activity of the receptors. A decrease in temperature at the vicinity of receptor cells resulted in a transient rise of the firing rate of the receptors, while the increase of temperature decreased the activity of the receptors.

Adaptation, Physiological↗
PubMed1992

Functional high efficiency expression of cloned leukocyte chemoattractant receptor cDNAs.

Human kidney 293 TSA cells were transfected by a calcium phosphate method with human formylpeptide and C5a receptor cDNAs with high efficiency. Formylpeptide receptor positive transfectants expressed a total of 968,000 +/- 34,000 receptors per cell with two affinity states (Kds of ca. 0.43 nM and 39 nM), which in the presence of 100 microM GTP gamma S decreased by ca. 4-fold the number of high-affinity sites. The ligand binding pharmacology of cloned and expressed formylpeptide receptors were indistinguishable from endogenous receptors on human neutrophils. Expressed formylpeptide and C5a receptors were functionally active in mobilizing intracellular calcium via a pertussis toxin sensitive mechanism with an ED50 for formylpeptide of ca. 0.5-1.0 nM. This expression system, in which receptor expression can be monitored by flow cytometric methods and in which intracellular calcium responses are measurable, unlike in the more popular COS-7 cell expression system, will provide a useful basis for the analysis of chemoattractant receptor structure-function relationships.

Base Sequence↗
PubMed2000

Zonal organization of the mammalian main and accessory olfactory systems.

Zonal organization is one of the characteristic features observed in both main and accessory olfactory systems. In the main olfactory system, most of the odorant receptors are classified into four groups according to their zonal expression patterns in the olfactory epithelium. Each group of odorant receptors is expressed by sensory neurons distributed within one of four circumscribed zones. Olfactory sensory neurons in a given zone of the epithelium project their axons to the glomeruli in a corresponding zone of the main olfactory bulb. Glomeruli in the same zone tend to represent similar odorant receptors having similar tuning specificity to odorants. Vomeronasal receptors (or pheromone receptors) are classified into two groups in the accessory olfactory system. Each group of receptors is expressed by vomeronasal sensory neurons in either the apical or basal zone of the vomeronasal epithelium. Sensory neurons in the apical zone project their axons to the rostral zone of the accessory olfactory bulb and form synaptic connections with mitral tufted cells belonging to the rostral zone. Signals originated from basal zone sensory neurons are sent to mitral tufted cells in the caudal zone of the accessory olfactory bulb. We discuss functional implications of the zonal organization in both main and accessory olfactory systems.

Animals↗
PubMed2006

A computational analysis of central CO2 chemosensitivity in Helix aspersa.

We created a single-compartment computer model of a CO(2) chemosensory neuron using differential equations adapted from the Hodgkin-Huxley model and measurements of currents in CO(2) chemosensory neurons from Helix aspersa. We incorporated into the model two inward currents, a sodium current and a calcium current, three outward potassium currents, an A-type current (I(KA)), a delayed rectifier current (I(KDR)), a calcium-activated potassium current (I(KCa)), and a proton conductance found in invertebrate cells. All of the potassium channels were inhibited by reduced pH. We also included the pH regulatory process to mimic the effect of the sodium-hydrogen exchanger (NHE) described in these cells during hypercapnic stimulation. The model displayed chemosensory behavior (increased spike frequency during acid stimulation), and all three potassium channels participated in the chemosensory response and shaped the temporal characteristics of the response to acid stimulation. pH-dependent inhibition of I(KA) initiated the response to CO(2), but hypercapnic inhibition of I(KDR) and I(KCa) affected the duration of the excitatory response to hypercapnia. The presence or absence of NHE activity altered the chemosensory response over time and demonstrated the inadvisability of effective intracellular pH (pH(i)) regulation in cells designed to act as chemostats for acid-base regulation. The results of the model indicate that multiple channels contribute to CO(2) chemosensitivity, but the primary sensor is probably I(KA). pH(i) may be a sufficient chemosensory stimulus, but it may not be a necessary stimulus: either pH(i) or extracellular pH can be an effective stimuli if chemosensory neurons express appropriate pH-sensitive channels. The lack of pH(i) regulation is a key feature determining the neuronal activity of chemosensory cells over time, and the balanced lack of pH(i) regulation during hypercapnia probably depends on intracellular activation of pH(i) regulation but extracellular inhibition of pH(i) regulation. These general principles are applicable to all CO(2) chemosensory cells in vertebrate and invertebrate neurons.

Acid-Base Equilibrium↗
PubMed2002

Differentiated response to sugars among labellar chemosensilla in Drosophila.

Recent findings have indicated that the Gr genes for putative gustatory receptors of Drosophila melanogaster are expressed in a spatially restricted pattern among chemosensilla on the labellum. However, evidence for a functional segregation among the chemosensilla is lacking. In this work, labellar chemosensilla were classified and numbered into three groups, L-, I- and S-type, based on their morphology. Electrophysiological responses to sugars and salt were recorded from all the accessible labellar chemosensilla by the tip-recording method. All the L-type sensilla gave good responses to sugars in terms of action potential firing rates, while the probability for successful recordings from the I-type and S-type sensilla was lower. No differences were found in the responses to sugars between chemosensilla belonging to the same type; however, dose-response curves for several different sugars varied among the sensilla types. The L-type sensilla gave the highest frequency of nerve responses to all the sugars. The I-type sensilla also responded to all the sugars but with a lower magnitude of firing rate than the L-type sensilla. The S-type sensilla gave a good response to sucrose, and lower responses to the other sugars. These results suggest that there might be variations in the expression level or pattern of multiple receptors for sugars among the three types of chemosensilla. The expression pattern of six Gr genes was examined using the Gal4/UAS-GFP system, and sensilla were identified according to the innervation pattern of each GFP-expressing taste cell. None of the spatial expression patterns of the six Gr genes corresponded to the sugar sensitivity differences we observed.

Action Potentials↗
PubMed1992

Attenuation of sensory receptor signaling by covalent modification.

The Tar receptor is a transmembrane protein that regulates bacterial chemotaxis in response to changes in the level of aspartic acid in the medium. The extracellular portion of the protein can bind aspartate, and the cytoplasmic portion modulates CheA kinase activity. The receptor can either activate or inhibit the kinase. The cytoplasmic portion of the receptor can be modified by carboxymethylation of specific glutamic acid residues. To test the effects of differential methylation on receptor function, we prepared membranes from cells that have specifically modified forms of the receptor and tested the relative ability of each of these forms to activate or inhibit CheA kinase. Completely demethylated receptor was a potent inhibitor and poor activator of the kinase, while the fully modified receptor was an excellent activator but an inefficient inhibitor. Partially modified receptor could act both as an effective inhibitor and as an activator. Reversible modification provides a mechanism that allows the cell to accumulate a population of receptor molecules capable of generating a wide range of signaling intensities.

Amino Acid Sequence↗
PubMed1997

Analysis and comparison of partial sequences of clones from a taste-bud-enriched cDNA library.

Differential patterns of cellular development and function are determined, at least in part, by the specific gene expression of particular cells. Thus, determination of differential patterns of gene expression between tissues is likely to help elucidate molecular details of tissue-specific processes. Our hypothesis was that cells of the circumvallate papilla involved in taste perception would express genes that are not expressed in the surrounding epithelium and that determination of the nature of these genes could be helpful in our understanding of the molecular details of taste. Using partial sequencing of clones derived from rat circumvallate papillae, we have begun to characterize genes that could be important in taste. We prepared a cDNA library of whole circumvallate papillae and, by means of a novel subtraction procedure, enriched taste-specific clones. Characterization of the libraries showed that subtraction resulted in good enrichment of taste-specific clones. Here we report the partial sequencing and analysis of 410 cDNA clones from the taste-bud-enriched cDNA library. Approximately 25% of the genes were identified on the basis of their high homology to known transcripts. These included the developmentally important molecules Pax-1, esp1, Notch 1, and Notch 3 that may play roles in the continuous turnover of taste receptor cells. A further 20% of the genes had no significant homology to known DNA sequences and were identified as taste-specific by Southern blot analysis.

Animals↗
PubMed1983

Mechanism of JH influence on the function of labellar chemosensilla in Phormia: experimental suggestions.

The aim of this research study was to determine at which level the JH effect of increasing chemosensillar sensitivity in Phormia could take place. Two-day-old adult female Phormia regina (Meigen) flies were used. Variations in electrical resistance and spike firing frequency of labellar chemosensilla stimulated with NaCl solutions were measured before and after topical application of a JH analogue (JHA). Variations in the above two parameters were also determined in a group of control flies. Results showed that an inverse linear relationship exists between electrical resistance and spike firing frequency in both JHA-treated and control flies. On this basis, we conclude that the above sensitivity variations depend on a mechanism common to both groups of flies. As regards the mode of action of this mechanism, we suggest that JH may influence the mucopolysaccharide secretory function of the accessory cells, the activity of which seems to account for changes in electrical resistance and therefore in sensitivity of the labellar chemosensilla.

Animals↗
PubMed2003

Peripheral coding of bitter taste in Drosophila.

Taste receptors play a crucial role in detecting the presence of bitter compounds such as alkaloids, and help to prevent the ingestion of toxic food. In Drosophila, we show for the first time that several taste sensilla on the prothoracic legs detect bitter compounds both through the activation of specific taste neurons but also through inhibition of taste neurons activated by sugars and water. Each sensillum usually houses a cluster of four taste neurons classified according to their best stimulus (S for sugar, W for Water, L1 and L2 for salts). Using a new statistical approach based on the analysis of interspike intervals, we show that bitter compounds activate the L2 cell. Bitter-activated L2 cells were excited with a latency of at least 50 ms. Their sensitivity to bitter compounds was different between sensilla, suggesting that specific receptors to bitter compounds are differentially expressed among L2 cells. When presented in mixtures, bitter compounds inhibited the responses of S and W, but not the L1 cell. The inhibition was effective even in sensilla where bitter compounds did not activate the L2 cell, indicating that bitter compounds directly interact with the S and W cells. Interestingly, this inhibition occurred with latencies similar to the excitation of bitter-activated L2 cells. It suggests that the inhibition in the W and S cells shares similar transduction pathways with the excitation in the L2 cells. Combined with molecular approaches, the results presented here should provide a physiological basis to understand how bitter compounds are detected and discriminated.

Animals↗
PubMed2001

Optical detection of neuromodulatory effects of conditioned taste aversion in the pond snail Lymnaea stagnalis.

Multiple site optical recording was used to analyze the neural activity changes caused by conditioned taste aversion (CTA) training in the pond snail Lymnaea stagnalis. In response to electrical stimulation of the median lip nerve, which transmits chemosensory signals of appetitive taste to the central nervous system, we optically detected large numbers of spikes in several parts of the buccal ganglion. The effects of CTA training on the spike responses were examined in two areas of the ganglion where the most active neural responses occurred. In one area (termed Area I) that included the N1 medial (N1M) cells, a class of central pattern generator interneurons involved in feeding behavior, the number of spikes in a period 1500-2000 ms after median lip nerve stimulation was significantly reduced in conditioned animals compared to control animals. In another area (termed Area II) positioned between buccal motoneurons, the B3 and B4CL (cluster) cells, the evoked spike responses were unaffected by CTA training. These results, taken together with our previous results indicating an enhancement of an inhibitory input to the N1M cells during CTA, suggest that an appetitive taste signal transmitted to the N1M cells through the median lip nerves is suppressed during CTA, resulting in a decrease of the feeding response.

Action Potentials↗
PubMed1985

Voltage- and current-clamp recordings of the receptor potential in olfactory receptor cells in situ.

Intracellular recordings obtained using the whole cell configuration of the patch recording technique show that isolated somas of olfactory receptor cells are electrogenic, producing fast overshooting action potentials when depolarized. In situ, these cells produce graded receptor potentials and action potentials when stimulated chemically. The receptor potential can be voltage clamped for analysis of the ionic basis of sensory transduction in olfaction.

Animals↗
PubMed1992

[Diurnal dynamics of red blood indicators after carotid glomectomy in rats].

After bilateral carotid glomectomy the rat resistance to acute hypoxia reduces and phenomena of anemia arise. There appear correlations between resistance to hypoxia and red cell count, hemoglobin and hematocrit. The diurnal fluctuation of rat resistance to acute hypoxia after the glomectomy does not change while hemodynamics undergo marked changes.

Acute Disease↗
PubMed1982

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.

Animals↗
PubMed1983

Effects of ischemia on the function and structure of the cat carotid body.

Interrupting the blood supply to the carotid body by ligating arteries of its vascular peduncle altered the chemoreceptive properties of the carotid nerve and produced structural changes in parenchymal (glomus and sustentacular) cells. The onset of ischemia was marked by an increase in the discharge of both A (myelinated) and C (unmyelinated) sensory fibers followed by depression and finally by receptor silence. The discharge of A-fibers disappeared after 30-50 min and that of C-fibers after 60-90 min. During ischemia of 15-60 min duration the threshold to pharmacological (NaCN, ACh) and 'natural' (hypoxic) stimuli progressively increased and was accompanied by reversible changes in the structure of parenchymal cells and nerve endings. Ischemia for 2 h or longer produced irreversible functional damage and disappearance of glomus and sustentacular cells from the carotid body. Following ischemic injury, nerve fibers regenerated and all responded to mechanical stimuli but only a few were stimulated by natural or pharmacological agents. Thus, parenchymal cells of the carotid body appear to be most important in transduction by allowing sensory fibers to respond to chemical stimuli.

Acetylcholine↗
PubMed1986

Suppression of mitotic activity and synchronization of cell development in olfactory epithelium.

Prolonged continuous application of hydroxyurea to frog olfactory epithelium suppresses mitotic activity in this tissue without side effects. After ZnSO4-induced coagulation necrosis of the olfactory epithelium, application of hydroxyurea prevents the usual epithelial regeneration. A method for obtaining frog olfactory epithelium with a developmentally synchronized neuronal population is introduced. The epithelium is first ablated by perfusion of the nasal cavity with ZnSO4. Then the epithelium is allowed to regenerate for 6 days, after which continuous introduction into the nasal cavity of hydroxyurea suppresses mitotic activity and thus the generation of new cells in the tissue. Cells formed during the 6 days prior to hydroxyurea treatment continue to develop. We found that the olfactory receptor cells are generated beginning on the 6th day after ablation, and so the epithelia contain a highly synchronized population of neurons all generated within about 24 h.

Animals↗
PubMed1985

[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.

Animals↗
PubMed1998

Maxillary palps can mediate taste rejection of plant allelochemicals by caterpillars.

All caterpillars possess a pair of maxillary palps that "drum" the surface of foods during feeding. These chemosensory organs contain over 65% of a caterpillar's taste receptor cells, but their functional significance remains largely unknown. We examined their role in rejection of plant allelochemicals, using the tobacco hornworm (Manduca sexta) as a model insect and an extract from a plant species (Grindelia glutinosa) as a model stimulus. We selected this system because hornworms reject foods containing Grindelia extract, and because preliminary studies indicated that their maxillary palps respond to this extract. We hypothesized that Grindelia extract elicits rejection through stimulating: (1) olfactory receptor cells, (2) taste receptor cells, (3) oral mechanoreceptors, and/or (4) a postingestive response mechanism. Our results were consistent only with hypothesis 2: caterpillars approached Grindelia-treated diets without apparent hesitation, but rejected it within 6 s of initiating biting; Grindelia-treated solutions stimulated taste receptor cells in the maxillary palp, but not the other gustatory chemosensilla; and ablating the maxillary palps eliminated rejection of Grindelia-treated diets. Our results demonstrate that taste receptor cells in the maxillary palps mediate rejection of Grindelia extract, and provide the first direct evidence for the role of maxillary palps in rejection of plant allelochemicals.

Action Potentials↗