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PubMed1998

Sugar cell responses to lactose and sucrose in labellar and tarsal taste hairs of Musca domestica.

Receptor cell responses in the largest labellar (LL) and tarsal (D) taste hairs of the housefly Musca domestica were investigated electrophysiologically using the tip-recording technique. In LL hairs, test series with lactose in concentrations of 12.5-400 mmol.l-1 yielded a threshold concentration around 12 mmol.l-1 and a calculated concentration eliciting half-maximal response of around 40 mmol.l-1, the maximal response varying between 18 and 30 impulses/300 ms. D hairs are more sensitive towards lactose, indicated by a slightly lower threshold and a by 60% higher response to 400 mmol.l-1 lactose. The high variation in the relative stimulating effectiveness of lactose and sucrose and experiments with sugar mixtures imply that these sugars bind to different receptor sites without noticeable cross affinity. A comparison of the concentration response characteristics for sucrose and lactose in LL and D hairs suggests that sucrose can combine with more than one site type, expressed in different proportions in both hair types. Results obtained with p-nitrophenyl-beta-galactoside as stimulus indicate that a beta-galactoside link is not sufficient for a substance to interact specifically with the lactose binding site. The exceptional lactose sensitivity of the sugar cell in M. domestica is discussed in the context of food acquirement and digestion.

Animals↗
PubMed1976

Axon regeneration following a lesion of the carotid nerve: electrophysiological and ultrastructural observations.

Carotid nerves of the cat were crushed and allowed to regenerate in order to study the properties of regerating fibers and the role of carotid body parenchymal cells (glomus or type I, and sustentacular or type II) in the transduction of chemosensory activity. Such activity is reinitiated 6 days after the nerves are crushed close (1-2 mm) to the carotid body. The process of recovery is delayed when a crush is made at successively greater distances (5-6 and 10-12 mm) from the carotid body. Ultrastructural studies show that the reappearance of nerve endings on the glomus-sustentacular cell complex coincides in time with the onset of chemosensory activity. The regenerated nerve endings increase in size and number and appear normal by 48 days. Some barosensory activity can be elicited 6 days after a nerve crush close to the carotid sinus, but rhythmic barosensory discharges only occur after the 21st day when myelinated axons reappear in the carotid sinus adventitia. Results suggest that recovery of chemosensory function depends on the reestablishment of apposition between regenerating carotid nerve fibers and parenchymal cells of the carotid body.

Animals↗
PubMed1995

Is nestin a marker for chemosensory precursor cells?

The vomeronasal and olfactory systems are unique in that their chemosensory neurons undergo continuous neurogenesis after development. Immunoreactivity to nestin, a neuronal precursor marker protein, was investigated in the developing rat vomeronasal organ to determine its potential as a cell marker. From postnatal day 1 (P1) to P22, the distribution of nestin positive cells became progressively restricted to the area adjacent to the basement membrane. By P29, the vomeronasal organ reached structural maturity and only a few nestin positive cells were observed. Results suggest that nestin may be a useful marker for neuronal precursor cells in studies of neurogenesis and development of chemosensory systems.

Animals↗
PubMed2004

The nose knows who's who: chemosensory individuality and mate recognition in mice.

Individual recognition is an important component of behaviors, such as mate choice and maternal bonding that are vital for reproductive success. This article highlights recent developments in our understanding of the chemosensory cues and the neural pathways involved in individuality discrimination in rodents. There appear to be several types of chemosensory signal of individuality that are influenced by the highly polymorphic families of major histocompatibility complex (MHC) proteins or major urinary proteins (MUPs). Both have the capability of binding small molecules and may influence the individual profile of these chemosignals in biological fluids such as urine, skin secretions, or saliva. Moreover, these proteins, or peptides associated with them, can be taken up into the vomeronasal organ (VNO) where they can potentially interact directly with the vomeronasal receptors. This is particularly interesting given the expression of major histocompatibility complex Ib proteins by the V2R class of vomeronasal receptor and the highly selective responses of accessory olfactory bulb (AOB) mitral cells to strain identity. These findings are consistent with the role of the vomeronasal system in mediating individual discrimination that allows mate recognition in the context of the pregnancy block effect. This is hypothesized to involve a selective increase in the inhibitory control of mitral cells in the accessory olfactory bulb at the first level of processing of the vomeronasal stimulus.

Animals↗
PubMedDate not supplied

A role for the yeast actin cytoskeleton in pheromone receptor clustering and signalling.

The development of cell polarity in response to external stimuli is a feature of most eukaryotic cell types. Haploid cells of the budding yeast Saccharomyces cerevisiae secrete peptide pheromones to induce conjugation with cells of the opposite mating type. Pheromone binding triggers transcription of mating-specific genes, cell cycle arrest in the G1 phase and the formation of a mating projection oriented toward the source of pheromone [1-2]. Based on a multitude of studies in diverse eukaryotic cells, it has been hypothesized that hierarchies of proteins function to govern the generation of cell polarity [3-4]. Numerous proteins have been identified in yeast that accumulate both at a position on the cell cortex that will develop into a mating projection in response to pheromone binding and at the site of bud formation in response to an intrinsic cue during mitotic growth. When the actin cytoskeleton is disrupted before bud formation by the addition of latrunculin-A (LAT-A), several proteins involved in budding, including the GTPase Cdc42p, are still able to achieve their appropriate polarized localization [5]. In contrast, we show here that following pheromone addition, an intact actin cytoskeleton is required for localization of several proteins to a discrete position on the cell cortex. We also demonstrate a role for actin in pheromone-induced receptor clustering and signalling. We propose that actin-mediated pheromone receptor clustering might consolidate signalling from Cdc42p to one region of the cell cortex so that small differences in receptor occupancy across the cell surface can be amplified into dramatic cellular polarity.

Actins↗
PubMed1978

Carotid body chemoreceptor function: hypothesis based on a new circuit model.

Integration of our own morphological observations into recent ultrastructural, biochemical, and neuropharmacological results on the carotid body led to a new hypothesis on chemoreceptor function: (i) Glomus cells with small dense-cored vesicles (type IB cells) that store norepinephrine are chemoreceptors. (ii) Glomus cells with large dense-cored vesicles (type IA), which are postsynaptic to the other glomus cell type and presynaptic to afferent nerve endings, are dopaminergic interneurons that suppress the afferent discharge frequency during normoxia by releasing dopamine. (iii) The hypoxic stimulus causes the chemoreceptive cell to release the stored norepinephrine, which in turn brings about disinhibition of the afferent nerve endings by inhibition of the interneuron. (iv) Afferent nerve endings and interneurons interact through reciprocal synapses that form a short inhibitory feedback loop. We propose that information in the carotid body is processed in a fashion graded rather than digital, providing a fine adjusted cooperation of all elements.

Afferent Pathways↗
PubMed1998

New aspects of chemoreception in flies.

For studies of insect taste the sensory cells of labellar taste hairs on the proboscis of calliphorid flies (e.g., Phormia) are preferred objects. Three sensory cells are electrophysiologically characterized: a sugar cell, a water cell and a cation or salt cell. Studying hairs on legs and proboscis of other families of flies we recently obtained results that extend our knowledge about the complexity of food detection in flies. The hoverfly Eristalis tenax (Syrphidae family) feeds on nectar and pollen of flowers. While nectar is recognized via the sugar cell, the so-called salt cell is activated by low concentrations of a water-soluble substance in extracts of pollen. From several tested pollen constituents only proline, an essential amino acid for pollen germination, stimulates the salt cell. The discrimination between salt and pollen in behavioral tests can be explained by the finding that the water cell remains active in the presence of pollen extract, but is inhibited by salts. Obviously the water cell activity is involved in the feeding decision. We already described a similar situation in Phormia, where the salt cell activity only elicits feeding behavior when the water cell is active too. In contrast to the sugar cells of species of flies studied so far the sugar cell of the house fly Musca domestica (Muscidae family) is highly sensitive to lactose, a disaccharide (beta-galactoside (1-->4) glucoside) naturally occurring only in the milk of mammals. Thus sugar spectra adapt to special environmental food situations. The fifth tarsomere of the forelegs of Musca bears besides two D-hairs 46 hairs of the B-type. The B-hairs are functionally not uniform in contrast to their structural identity. Only two hairs, the 'water hairs,' contain a water cell beside a spontaneously firing cell, but no sugar cell. Other examples of diversity are hairs that contain apart from the classical sugar cells, additional cells which react either to p-nitrophenyl-beta-galactoside, but not to the chemically related lactose, or to p-nitrophenyl-alpha-glucoside. Therefore the rule established for the labellar taste hairs that each hair type contains the same physiological equipment of sensory cells, does not hold for the taste hairs of the legs.

Animals↗
PubMed1982

Ionic mechanism for the osmotically-induced depolarization in neurones of the guinea-pig supraoptic nucleus in vitro.

1. Effects of hypertonic solutions prepared by adding NaCl or sucrose to Krebs solution on intracellular potentials were observed in neurones of the supraoptic nucleus using brain slices of the guinea-pig hypothalamus. 2. Hypertonic solutions (306-488 m-osmole/kg) depolarized the membrane, increased the input resistance and augmented the spontaneous firing rate in supraoptic neurones, whereas cells in the hippocampus and anterior or ventromedial hypothalamus were not affected by the hypertonic solutions. 3. The excitatory action of hypertonic solutions on supraoptic neurones was retained in the medium containing 0 mM-Ca2+ and 12 mM-Mg2+. 4. Amplitude of the depolarization induced by superfusion of hypertonic solutions was voltage-dependent. The reversal potential for the depolarization was about -90 mV. 5. The reversal potential for the depolarization induced by hypertonic solution shifted as a function of [K+]0. 6. These results suggest that the supraoptic neurones are themselves osmosensitive and that the local osmotic-related information is transduced to neural signals in these cells by alteration in the membrane ionic permeability, probably due to suppression of K+ conductance.

Animals↗
PubMed1989

The cell biology of vertebrate taste receptors.

New technologies in neurophysiology and ultrastructural research are bringing about rapid advances in our understanding of taste, particularly at the cellular level. The model of chemosensory processing in the taste bud presented here can now be explored in great detail. The synaptic organization of the taste bud indicates a potential for intriguing peripheral integrative mechanisms, including cross-talk between taste cells, summation of chemoreceptor responses by interneurons (basal cells) in the taste bud, and centrifugal control of taste buds via efferent input from the CNS. Figure 2 summarizes these findings. The existence of voltage-gated ionic channels on taste cells and their unequal distribution in apical and basolateral membrane suggests mechanisms for chemosensory transduction: A primary event in the transduction process for many taste stimuli is likely to be the closure of apical potassium channels, thus leading to a depolarizing receptor potential. The closure of these apical potassium channels is probably mediated via cyclic nucleotides or intracellular Ca2+.

Animals↗
PubMed1993

Localization of cholecystokinin-like and calcitonin-like peptides in infant carotid bodies: a light- and electron-microscopic immunohistochemical study.

Previous immunohistochemical studies have identified several regulatory peptides in the carotid body chief cells in both humans and animals. These peptides, together with amines, may be important in the modulation of the chemoreflex by the carotid body. We report the localization and distribution of calcitonin and cholecystokinin-like (CCK) immunoreactivity in chief cells of human infant carotid body by light- and electron-microscopic immunohistochemical techniques. Consecutive sections immunostained with calcitonin and/or CCK antibodies revealed positively stained chief cells, both alone and in clusters, scattered throughout the carotid body lobule. Generally more chief cells were positive for calcitonin than for CCK. This was confirmed by quantitative analysis showing that the ratio of calcitonin to CCK immunoreactive cells was consistently > 2:1 in all cases studied. There was no apparent correlation between the immunoreactivity for the two peptides and the age, sex, or postmortem interval. Calcitonin-like and CCK-like immunoreactivities were localized electron-microscopically over the dense core granules of the chief cells. Calcitonin and CCK-like peptides in carotid body chief cells may act as neurotransmitters or neuromodulators involved in chemoreception.

Calcitonin↗
PubMed1994

Taste responses of bullfrog to pungent stimuli.

Taste responses of bullfrogs to various pungent compounds and taste substances were electrophysiologically recorded from glossopharyngeal nerves. The threshold concentrations were approximately 10(-7) M for piperine, approximately 10(-6) M for capsaicin and approximately 10(-4) M for allyl isothiocyanate. At any concentration examined, piperine was more potent than capsaicin. Both piperine and capsaicin elicited desensitizing responses, but the taste receptors recovered from the desensitization within 10 min after washing with deionized water. Cross-adaptation experiments revealed that capsaicin only partially desensitizes receptors for piperine, L-leucine, HCl or quinine. Perfusion of the lingual artery with a solution containing no added Ca decreased the responses to capsaicin. Such a solution has been shown to suppress the taste nerve responses by blocking synaptic transmissions between taste cells and taste nerves [8]. These results suggest that the gustatory effects of capsaicin are different from its pharmacological effects on sensory neurons. It is likely that capsaicin and other pungent compounds, when they act as seasonings, stimulate taste cells rather than the free nerve endings of the sensory neurons.

Adaptation, Physiological↗
PubMed1993

CO2 chemoreception in the pulmonate snail, Helix aspersa.

We have studied the response of the pneumostome to CO2, O2 and combined CO2 and O2 in intact snails. We found that pneumostomal opening increases in response to both hypercapnia and mild hypoxia. We determined which neural structures were essential for the pneumostomal response to CO2 by eliminating parts of the nervous system: the subesophageal ganglia and an intact anal nerve were necessary and sufficient elements for the CO2 response. Within the subesophageal ganglia, we identified a discrete region on the medial margin of the visceral ganglion that was capable of increasing pneumostomal area when focally stimulated with 6% CO2. Ion substitution experiments indicated that pneumostomal responses to hypercapnia were not mediated by the pneumostomal motor neurons themselves, but rather by interneurons connected polysynaptically to the motor neurons controlling pneumostomal function. In conclusion, intact H. aspersa have a ventilatory response to CO2, and this response is mediated by CO2 sensitive cells located in a small area of the central nervous system.

Animals↗
PubMed1998

Suppression of glomus cell K+ conductance by 4-aminopyridine is not related to [Ca2+]i, dopamine release and chemosensory discharge from carotid body.

The hypothesis that suppression of O2-sensitive K+ current is the initial event in hypoxic chemotransduction in the carotid body glomus cells was tested by using 4-aminopyridine (4-AP), a known suppressant of K+ current, on intracellular [Ca2+]i, dopamine secretion and chemosensory discharge in cat carotid body (CB). In vitro experiments were performed with superfused-perfused cat CBs, measuring chemosensory discharge, monitoring dopamine release by microsensors without and with 4-AP (0.2, 1.0 and 2.0 mM in CO2-HCO3- buffer) and recording [Ca2+]i by ratio fluorometry in isolated cat and rat glomus cells. 4-AP decreased the chemosensory activities in normoxia but remained the same in hypoxia and in flow interruption. It decreased the tissue dopamine release in normoxia, and showed an additional inhibition with hypoxia. Also, 4-AP did not evoke any rise in [Ca2+]i in glomus cells either during normoxia and hypoxia, although hypoxia stimulated it. Thus, the lack of stimulatory effect on chemosensory discharge, inhibition of dopamine release and unaltered [Ca2+]i by 4-AP are not consistent with the implied meaning of the suppressant effect on K+ current of glomus cells.

4-Aminopyridine↗
PubMed1993

Protein kinase C sensitizes olfactory adenylate cyclase.

Effects of neurotransmitters on cAMP-mediated signal transduction in frog olfactory receptor cells (ORCs) were studied using in situ spike recordings and radioimmunoassays. Carbachol, applied to the mucosal side of olfactory epithelium, amplified the electrical response of ORCs to cAMP-generating odorants, but did not affect unstimulated cells. A similar augmentation of odorant response was observed in the presence of phorbol dibutyrate (PDBu), an activator of protein kinase C (PKC). The electrical response to forskolin, an activator of adenylate cyclase (AC), was also enhanced by PDBu, and it was attenuated by the PKC inhibitor Goe 6983. Forskolin-induced accumulation of cAMP in olfactory tissue was potentiated by carbachol, serotonin, and PDBu to a similar extent. Potentiation was completely suppressed by the PKC inhibitors Goe 6983, staurosporine, and polymyxin B, suggesting that the sensitivity of olfactory AC to stimulation by odorants and forskolin was increased by PKC. Experiments with deciliated olfactory tissue indicated that sensitization of AC was restricted to sensory cilia of ORCs. To study the effects of cell Ca2+ on these mechanisms, the intracellular Ca2+ concentration of olfactory tissue was either increased by ionomycin or decreased by BAPTA/AM. Increasing cell Ca2+ had two effects on cAMP production: (a) the basal cAMP production was enhanced by a mechanism sensitive to inhibitors of calmodulin; and (b) similar to phorbol ester, cell Ca2+ caused sensitization of AC to stimulation by forskolin, an effect sensitive to Goe 6983. Decreasing cell Ca2+ below basal levels rendered AC unresponsive to stimulation by forskolin. These data suggest that a crosstalk mechanism is functional in frog ORCs, linking the sensitivity of AC to the activity of PKC. At increased activity of PKC, olfactory AC becomes more responsive to stimulation by odorants, forskolin, and cell Ca2+. Neurotransmitters appear to use this crosstalk mechanism to regulate olfactory sensitivity.

Adenylyl Cyclases↗
PubMed2001

An artificial sweetener stimulates the sweet taste in insect: dual effects of glycyrrhizin in Phormia regina.

Glycyrrhizin, found in the root of licorice (Glycyrrhizia glabra), has been used extensively as a non-sugar sweetener for humans and also as a medicine. As far as we know, the present work is the first report describing that a non-sugar sweetener for humans induces a sweet taste in insects. In behavioural experiments, we found that glycyrrhizin induced the feeding response, including full proboscis extension in the blowfly, Phormia regina. Glycyrrhizin also induced impulses of the sugar receptor cell in the labellar chemosensillum, which is highly specialized for the tastes of sugars and nucleotides. The optimum concentration of glycyrrhizin was 3.0 mM, which is much lower than that of sucrose. It has been established that multiple receptor sites, the pyranose receptor site (P site) and the furanose receptor site (F site), are present in the sugar receptor cell of the blowfly and the fleshfly. The inhibitors specific to the P site, starch and PCMB (p-chloromercuribenzoate), partially inhibited glycyrrhizin-induced responses but not levan (an inhibitor to the F site), indicating that the P site on the sugar receptor cell is involved in the glycyrrhizin action but not the F site. When 30 s stimulation with 3.0 mM glycyrrhizin was repeated with an interval of 3--10 min, the impulse frequency to the second stimulus was higher than that to the first one and doubled within 6 min. The first stimulus lasting longer than 10 s potentiated the impulse generation and reduced the adaptation rate during the second stimulus. These results suggest that, in addition to the action via the P site, an additional mechanism, possibly in the signal transduction cascade of the sugar receptor cell, may be involved in the action of glycyrrhizin.

Adaptation, Physiological↗
PubMed2005

Biochemical and physiological evidence that calmodulin is involved in the taste response of the sugar receptor cells of the blowfly, Phormia regina.

The gustatory system is essential for almost all animals. However, the signal transduction mechanisms have not yet been fully elucidated. We isolated labellar chemosensilla from blowfly, Phormia regina, and purified calcium binding proteins from the water soluble fraction. The most abundant calcium-binding protein was calmodulin. To investigate the role of calmodulin in taste transduction, electrophysiological responses were recorded with the calmodulin inhibitor, W-7. When we stimulated the labellar chemosensillum with sucrose plus W-7, a dose-dependent decrease of impulse frequency was observed when the concentration was <50 microM. In addition, when W-7 at 50 microM or higher concentration was added, an initial short-term impulse generation from the sugar receptor cell was observed, but this was followed by a silent period. When the sensillum was stimulated with W-7 plus a membrane-permeable cGMP analog, dibtyryl-cGMP or 8-bromo-cGMP, impulses of the sugar receptor cell were induced but the frequency was decreased. By the sidewall-recording method, we observed that the receptor potential induced by sucrose stimulation was decreased by W-7 in the sugar receptor cell, and corresponded with a disappearance of impulses. These data strongly suggest that the cGMP-gated channel generating receptor potential in the sugar receptor cell requires calmodulin for its gating.

Animals↗
PubMed2000

Chemosensory signal transduction in paramecium.

Paramecia are ciliated single-cell eukaryotic organisms that can respond to chemical cues in their environment. Glutamate is among those cues, which attract cells. We describe briefly here the following attributes of glutamate chemoresponse: 1) Cells are attracted to L-glutamate relative to KCl at high concentrations of glutamate. 2) There are at least two specific, relatively low affinity glutamate binding sites on the cell surface. Glutamate can be displaced from only one of the binding sites by inosine monophosphate (IMP), and quisqualate displaces glutamate from the second site, which is likely to be the glutamate receptor involved in attraction to glutamate. 3) IMP is a repellent and does not act synergistically with glutamate, whereas guanosine monophosphate (GMP) does. 4) Similarly, glutathione is an attractant, but glutamate and glutathione appear to use different transduction pathways. 5) Glutamate hyperpolarizes the cell. The ionic mechanism is not yet verified, but is likely to involve a K conductance. 6) Glutamate induces a rapid and robust increase in cAMP in the cell. Protein kinase A (PKA) is possibly involved in the transduction pathway because kinase inhibitors such as H7 and H8 inhibit glutamate response, but do not affect responses to other attractants, such as acetate and ammonium. Activation of PKA by the rapid rise in cAMP may sustain the hyperpolarization phosphorylation and activation of the plasma membrane calcium pump. 7) Candidate glutamate binding proteins are being identified among the cell surface proteins with the use of affinity chromatography.

Animals↗