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PubMed1991

Mixture suppression in behavior: the antennular flick response in the spiny lobster towards binary odorant mixtures.

The behavioral responses of Florida spiny lobsters towards various concentrations of binary mixtures and their constituents (AMP, betaine, cysteine, succinate, and taurine) were measured using an antennular flicking assay. The rate of flicking increases with dose and has low thresholds: flick rates towards each of the five chemicals increased with concentration with thresholds between 1 nM and 100 microM. A mixed receptor composition model, which incorporates knowledge of the composition of receptor site types and their distribution across receptor cells (15), was used to predict responses to binary mixtures based on responses to the individual constituents. Nine of the ten binary mixtures elicited response magnitudes which were less than predicted by this model, suggesting mixture suppression. These mixture interactions appear to be independent of the concentration of the mixture tested; rather, they occur with the same magnitude at all concentrations. These behavioral results corroborate findings in olfactory receptor cell studies which indicate the significant prevalence of mixture suppression towards some of the same binary mixtures (19,20).

Animals↗
PubMed2001

A candidate taste receptor gene near a sweet taste locus.

The mechanisms underlying sweet taste in mammals have been elusive. Although numerous studies have implicated G proteins in sweet taste detection, the expected G protein-coupled receptors have not been found. Here we describe a candidate taste receptor gene, T1r3, that is located at or near the mouse Sac locus, a genetic locus that controls the detection of certain sweet tastants. T1R3 differs in amino acid sequence in mouse strains with different Sac phenotypes ('tasters' versus 'nontasters'). In addition, a perfect correlation exists between two different T1r3 alleles and Sac phenotypes in recombinant inbred mouse strains. The T1r3 gene is expressed in a subset of taste cells in circumvallate, foliate and fungiform taste papillae. In circumvallate and foliate papillae, most T1r3-expressing cells also express a gene encoding a related receptor, T1R2, raising the possibility that these cells recognize more than one ligand, or that the two receptors function as heterodimers.

Alleles↗
PubMed1984

Processing of olfactory information at three neuronal levels in the spiny lobster.

Odor quality coding was analyzed at three neuronal levels, receptor cells and two levels of chemosensory interneurons, in the olfactory system of the spiny lobster Panulirus argus . Responses to three of the most stimulatory compounds for this animal - taurine, glutamate and betaine - were recorded at each level in order to compare basic neuronal response properties, single cell and population response spectra, and across-neuron patterns. Mean response specificity increased for cells at each successive neuronal level. The increase in breadth of tuning between receptor cells and low-order interneurons was paralleled by an increase in interstimulus across-neuron correlations. However, in high-order interneurons, there was a relative decline in across-neuron correlations, indicating that the more broadly-tuned high-order interneurons are better able to discriminate between any two compounds than are the more narrowly-tuned low-order interneurons. Although stimulus quality appears to be coded by interneurons as an across-fiber pattern, the fact that some low-order and high-order interneurons retained the narrow specificity of receptor cells suggests that labeled lines may have an important function in coding throughout the olfactory pathway of the spiny lobster.

Animals↗
PubMed2000

Localization of hindbrain glucoreceptive sites controlling food intake and blood glucose.

Feeding and blood glucose responses to local injection of nanoliter volumes of 5-thio-D-glucose (5TG), a potent antimetabolic glucose analogue, were studied at 142 hindbrain and 61 hypothalamic cannula sites. A site was considered positive if 5TG elicited at least 1.5 g more food intake or a hyperglycemic response at least 25 mg/dl greater than the respective responses elicited by vehicle injection in the same rat. Of 61 hypothalamic cannula sites tested, none were positive for blood glucose and only one was positive for feeding. Increasing the 5TG dose to 48 ug did not produce additional positive results at hypothalamic sites. In contrast, 66 hindbrain sites were positive for feeding and 49 were positive for blood glucose, with 33 of these being positive for both responses. The distribution of positive sites for feeding and hyperglycemia overlapped almost completely. Positive sites were concentrated in two distinct zones: one in the ventrolateral and one in the dorsomedial medulla. In both locations, the glucoreceptive areas extended approximately from the level of the area postrema (AP) to the pontomedullary junction. Glucoreceptive zones were co-distributed with epinephrine cell groups C1-C3, suggesting that epinephrine neurons may be important components of the neural circuitry for glucoregulation. Localization of glucoreceptive sites will facilitate positive identification of glucoreceptor cells and the direct analysis of the neural mechanisms through which they influence food intake and metabolic responses.

Animals↗
PubMed1999

Molecular analysis of the pheromone and pheromone receptor genes of Ustilago hordei.

Cell-cell signaling is an integral part of the sexual and disease cycles of the smut fungi, which must mate to be pathogenic. This study reports the cloning and characterization of the pheromone genes Uhmfa1 and Uhmfa2 from MAT-1 and MAT-2 mating types of U. hordei, respectively, and the pheromone receptor gene Uhpra2 from MAT-2 cells. Similar to other fungal pheromone genes, Uhmfa1 and Uhmfa2 encode precursor peptides. Uhpra2 encodes a protein with sequence similarity to the 7-transmembrane class of G-protein coupled receptors. Deletion of Uhmfa1 and Uhpra1, and their subsequent replacement, confirmed the role of these genes in initiation of the sexual cycle. Uhmfa1 and Uhmfa2 were differentially expressed in various cell types and when opposite mating-type cells were grown together. The predicted mature pheromones of each mating type were synthesized, and each specifically induced conjugation tube formation in cells of the opposite mating type.

Amino Acid Sequence↗
PubMed1991

Regulation of HIV-1 gene expression.

The quantity and quality of HIV-1 gene expression is temporally controlled by a cascade of sequential regulatory interactions. Basal HIV-1 transcription is determined by interaction of cellular regulatory proteins with specific DNA target sequences within the HIV-1 long-terminal repeat. The most notable of these protein:DNA interactions involves NF-kappa B, a transcription factor that plays a pivotal role in the activation of genes important for cellular responses to infection and inflammation. A second level of control involves the virally encoded Tat trans-activator. Tat, in combination with as yet unidentified cellular proteins, activates HIV-1 gene expression through a specific interaction with the viral TAR RNA stem-loop target sequence. A final level of regulation is mediated by the viral Rev protein. Rev acts posttranscriptionally to induce the expression of HIV-1 structural proteins and thereby commits HIV-1 to the late, cytopathic phase of the viral replication cycle. Rev activity appears to require a critical, threshold level of Rev protein expression, thus preventing entry into this late phase in cells that are unable to support efficient HIV-1 gene expression. In total, this cascade of regulatory levels allows the HIV-1 provirus to respond appropriately to the intracellular milieu present in each infected cell. In activated cells, the combination of Tat and Rev can stimulate a very high level of viral gene expression and replication. In quiescent or resting cells, in contrast, these same regulatory proteins are predicted to maintain the HIV-1 provirus in a latent or nonproductive state.

Avian Leukosis Virus↗
PubMed1985

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.

Animals↗
PubMed1996

Identification of osmoresponsive neurons in the forebrain of the rat: a Fos study at the ultrastructural level.

The aims of this study are twofold. The first is to describe the ultrastructural morphology of putative osmoreceptors concentrated in the ventral aspect of the lamina terminalis in the rat forebrain. The second is to determine whether or not these neurons lie within an area which lacks a blood-brain barrier, i.e. the organum vasculosum lamina terminalis. The results describe a compact population of neurons in the ventral part of the lamina terminalis which both respond to an osmotic challenge and project directly to the supraoptic nucleus. Injection of horseradish peroxidase into the circulation, as a marker to define areas of the brain without a blood-brain barrier, indicates that these neurons are in the dorsal aspect of the organum vasculosum of the lamina terminalis. An ultrastructural analysis of the neurons in this area, which respond to an osmotic challenge with an elevation of Fos protein, show them to have no specific morphological characteristics which differentiate them from other, non-responsive neurons in the organum vasculosum of the lamina terminalis. However, one possible exception is that osmotically sensitive neurons have a less indented nucleus, suggesting that they are in a more active state than their non-osmotically sensitive neighbours. It is concluded that neurons in this region of the brain are candidate structures for the "receptors" which mediate vasopressin release in response to an osmotic challenge. The response of only a subset of neurons in the organum vasculosum of the lamina terminalis to an osmotic stimulus, despite an apparent morphological homogeneity and the ability of blood borne agents to reach all parts of the structure suggests that osmoresponsiveness is conferred by unique membrane properties or intracellular processing events. The presence of synaptic input to osmoresponsive cells indicates a potential for integration of other inputs at this level.

Animals↗
PubMedDate not supplied

Neural regulation of sympathetic nerve activity in heart failure.

One of the hallmarks of chronic congestive heart failure is an increase in sympathetic tone to the peripheral circulation and to the heart. A correlation between plasma norepinephrine and the severity of the heart failure state has been demonstrated. One mechanism that has been proposed to account for this sympathoexcitation is a depression in the baroreflex and, perhaps, cardiac reflex control of sympathetic nerve activity. This review summarizes work from several laboratories, including our own, that documents a depressed baroreflex control of heart rate and sympathetic nerve activity in both animals and humans with heart failure. The mechanism of the depressed baroreflex most likely is caused by reduced baroreceptor sensitivity as well as enhanced input to the central nervous system from cardiac receptors that are chemosensitive. Although sympathetic tone and arterial baroreflex sensitivity are altered in heart failure, there have been no studies showing a cause-and-effect relationship. Increases in plasma norepinephrine are similar in baroreceptor-denervated and intact dogs paced into heart failure. This latter observation cells into question the traditional concept of baroreceptor-mediated increases in sympathetic tone in heart failure.

Animals↗
PubMed1999

Neuroepithelial bodies as airway oxygen sensors.

Since the discovery of neuroepithelial bodies (NEB) in the late 1930s, evidence has accumulated to suggest that these cells may function as hypoxia-sensitive airway sensors. Until recently, this hypothesis was based largely on morphological observations. The use of in vitro models of isolated NEB, combined with electrophysiological approaches, have provided direct evidence that NEB cells express a membrane-bound O2 sensor and are the transducers of hypoxic stimulus. Here, we review the historical evidence and current state of knowledge of the oxygen-sensing properties of NEB cells, comparison with other O2 sensing cells, as well as recent advances that have been made using molecular and electrophysiological techniques. The possible role of NEB in perinatal pulmonary pathophysiology is also discussed.

Animals↗
PubMed2001

Immunocytochemical study of G(i)2alpha and G(o)alpha on the epithelium surface of the rat vomeronasal organ.

To investigate in detail the distribution of G protein subtypes G(i)2alpha and G(o)alpha along the surface of the vomeronasal epithelium, we used double labeling immunocytochemical methods and electron microscopy. We examined the immunoreactivity of these surface structures with antibodies against G(i)2alpha and G(o)alpha. G(i)2alpha- and G(o)alpha-positive cells were observed at the epithelial surface and were evenly distributed. Electron microscopy revealed that strong immunoreactivities to both antibodies were observed on the microvilli and knob-like surface structures of receptor cells. No immunoreactivity was found on the microvilli or surface membranes of supporting cells. This expression pattern is similar to that reported for putative pheromone receptors. These data confirm that there are two distinct classes of vomeronasal receptor cells expressed at the surface of the epithelium. These two classes of receptors correspond to the same G(i)2alpha- and G(o)alpha-positive cells distributed in cell body layers of the epithelium and in the axon terminals in the accessory olfactory bulb.

Animals↗
PubMed1992

Intracellular pH and oxygen chemoreception in the cat carotid body in vitro.

To test the hypothesis that O2 chemoreception in the carotid body (CB) is mediated by cellular acidosis, we simultaneously measured responses of the chemosensory and intracellular pH (pHi) to agents that are known to change pHi and studied the effects of hypoxia and ischemia on these variables in the cat CB. The CB was perfused and superfused in vitro with a modified Tyrode's solution at 36.0 +/- 0.5 degrees C with or without CO2-HCO3- (pH 7.40) and equilibrated at a given PO2. Chemosensory discharges were recorded from the whole carotid sinus nerve. To measure pHi changes, the CB was loaded with the pH-sensitive indicator 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, and the fluorescence (excitation 420-490 nm, emission greater than 515 nm) was detected by an intensified charged coupled device camera with an epifluorescence macroscope. Boluses of Tyrode's solution (0.5 ml, free of CO2-HCO3-) containing sodium acetate or NH4Cl prolonged perfusion of acid Tyrode's solution (pH 7.20-6.50), and boluses of Tyrode's solution with CO2-HCO3- were used. A decrease of fluorescence indicated pHi turning acid, and an increase of fluorescence indicated a change in alkaline pHi. Chemosensory activity varied inversely with the fluorescence change after application of these agents. Interruption of perfusate flow or application of hypoxic perfusate resulted in large increases in chemosensory discharge without any change in the fluorescence. The results indicated that chemosensory responses to brief ischemia and hypoxia were not mediated by a fall of pHi of CB cells, whereas those to CO2 and extracellular acidity were associated with decreases in pHi.

Animals↗
PubMed1982

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.

Animals↗
PubMed1982

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.

Chemoreceptor Cells↗
PubMed1994

Evidence for calcium channels involved in regulating nematocyst discharge.

In the tentacles of sea anemones, nematocyst discharge is regulated by cnidocyte/supporting cell complexes (CSCCs) of which three functional types have been identified: A, B and C. Type A CSCCs respond to contact by vibrating targets. Types B and C CSCCs respond to contact by static targets. Whereas type C CSCCs respond to contact alone, type B CSCCs require that surface chemoreceptors bind ligands before becoming responsive. Reducing Ca2+ levels in artificial seawater to below 1 mM inhibits discharge from each type of CSCC. The calcium channel inhibitors, nifedipine or verapamil, selectively inhibit discharge from type B CSCCs. The calcium channel activator, Bay K-8644, mimics the biphasic dose response of type B CSCCs to natural chemosensitizers such as N-acetylated sugars. Discharge from type A CSCCs is unaffected by inhibitors of L-type calcium channels, but is selectively inhibited by the aminoglycoside antibiotics, gentamicin and streptomycin. While each type of CSCC requires extracellular calcium, the calcium channels employed may vary according to CSCC type.

Aminoglycosides↗
PubMed2002

Fine structure and immunocytochemistry of a new chemosensory system in the Chiton larva (Mollusca: Polyplacophora).

Combined electron microscopy and immunocytochemistry of the larvae of several polyplacophoran species (Chiton olivaceus, Lepidochitona aff. corrugata, Mopalia muscosa) revealed a sensory system new to science, a so-called "ampullary system." The cells of the "ampullary system" are arranged in four symmetrically situated pairs lying dorsolaterally and ventrolaterally in the pretrochal part of the trochophore-like larva and they send axons into the cerebral commissure. They are lost at metamorphosis. The fine structure of these cells strongly resembles that of so-called "ampullary cells" known from various sensory organs of other molluscs, such as the apical complex of gastropod and bivalve larvae, osphradia of vetigastropods, and olfactory organs of cephalopods, and nuchal organs of certain polychaetes. The ampullary cells and their nerves are densely stained by anti-FMRF-amide fluorescence dyes, whereas antiserotonin staining is only weak. While cytological homology of the ampullary cells with those of other organs is probable, the ampullary system as a whole is regarded as a synapomorphy of the Polyplacophora or Chitonida.

Animals↗
PubMed1979

Elimination of central chemosensitivity by coagulation of a bilateral area on the ventral medullary surface in awake cats.

Breathing and respiratory response to CO2 were observed in 6 awake cats and 1 control before and after bilateral coagulation of the formerly described area S (Schläfke and Loeschcke, 1967) on the ventral medullary surface under hyperoxic conditions. Ventilation decreased, PCO2 rose and CO2 response was almost or completely abolished in 4 cats, and moderately reduced in 2 cats. Inhalation of CO2 had an inhibitory effect on ventilation in two cases. In some instances the respiratory frequency was increased by CO2. Periodic breathing as well as spontaneous hyperventilation elicited by 'arousal' indicate parallels to the Pickwickian or Ondine's curse syndrome. No respiratory changes were produced by a lesion on the pyramidal tract medial to the area S. It is concluded that central chemosensitivity can be eliminated within the superficial layer of the area S. The loss of CO2 response seems to be correlated with complete destruction of the superficial nerve cells located within the area S (Petrovický, 1968) and degeneration within the ventral part of the nucleus paragigantocellularis.

Animals↗
PubMed1998

Chemoreceptive epithelioid cells in the chicken aorta. An electron microscopical study.

Aggregations of granulated epithelioid cells exist in the chicken aorta. In the present study, the locational characteristics of the epithelioid cells were investigated via an electron microscopic approach. Epithelioid cells were found mainly in two regions; the tunica interna just below the endothelial cell layers, and the intermediate region of the tunica media. In the former, the epithelioid cells were in contact with endothelial cells and sometimes directly exposed to the aortic lumen. No contact between the epithelioid cells and the nerve endings was observed in this region. On the other hand, in the intermediate region of the tunica media, five or more epithelioid cells were aggregated, and the synaptic structures were occasionally observed. Additionally, the epithelioid cells in this region was observed to closely contact smooth muscle cells. In an experiment using horseradish peroxidase injection, reactions were detected in the intercellular spaces between the epithelioid cells and endothelial cells. These results suggest that the epithelioid cells localized in the subendothelial region receive information from the aortic lumen, whereas their aggregations in the tunica media are controlled by the nervous system.

Animals↗