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At least 1,621 records · Page 90Linked to original sources
PubMed1982

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.

Animals↗
PubMed1975

A monoamine in the gustatory cell of the frog's taste organ: a fluorescence histochemical and electron microscopic study.

Fluorescence histochemistry reveals that in the frog's taste organ a yellow fluorescence is regularly observed at the most basal region of the sensory epithelium. The fluorescence has a strong intensity, but it fades rapidly upon the UV-irradiation. The peak of the emission spectrum is at 520 mmug. Following reserpine treatment the yellow fluroescence is markedly reduced, but not depleted completely. From these characteristics the monoamine fluorescence is regarded as representing 5-HT (serotonin). The ultrastructural study on sensory epithelia shows that the terminal portions of gustatory cell processes are localized at the basal region. These portions are filled with dense cored vesicles (700-1000 angstrom in diameter) and frequently opposed with nerve fibers penetrating into the epithelium. The gustatory cell processes are also interposed between the terminal portions of nerve fibers. The cytoplasm of the gustatory cell process is characterized by many mitochondria, fine filaments and glycogen particles, but contains few cored vesicles. The distribution of terminal portions of gustary cell processes seems to correspond fairly well to that of the monoamine fluorescence observed discontinuously along the basal lamina. Accordingly it is concluded that the fluorigenic monoamine is localized in the cored vesicles of the gustatory cell.

Animals↗
PubMed1995

Voltage-dependent sodium currents recorded from dissociated rat taste cells.

Voltage-dependent sodium currents were analyzed in detail from dissociated mammalian taste receptor cells using the whole-cell patch clamp technique. Approximately 50-75% of all taste receptor cells expressed sodium currents. These currents activated close to -50 mV (holding potential = -80 mV) with maximal currents most often occurring at -10 mV. The distribution of maximal inward currents across all cells appeared to display two peaks, at -254 pA and -477 pA, possibly due to differences in sodium channel density. Inward currents were eliminated by replacing 90% of external sodium with N-methyl-D-l-glucamine. The current-voltage relationship of the activated current, as measured by a tail current analysis, was linear, suggesting an ohmic nature of the open channel conductance. The relationship between the time to the peak activated current and the step potential was well fit by a double exponential curve (tau1 = 6.18, tau2 = 37.8 msec). Development of inactivation of the sodium current was dependent upon both voltage- and temporal-parameters. The voltage dependence of the time constant (tau) obtained from removal of inactivation, development of inactivation, and decay of the sodium current displayed a bell-shaped curve with a maximum of 55 msec at -70 mV. In addition to fast inactivation (half maximal at -50 mV), these currents also displayed a slow inactivation (half maximal at -65 mV). Voltage-dependent sodium currents were reversibly inhibited by nanomolar concentrations of tetrodotoxin (Kd = 10(-8) M). There was no evidence of a TTX-insensitive sodium current. This description broadens our understanding of gustatory transduction mechanisms with a particular relevance to the physiological role of receptor cell action potentials.

Animals↗
PubMed1985

The cathodal OFF response of electric taste in rats.

The cathodal OFF response in electric taste, the production of a taste sensation at the break of a microampere cathodal current passed through the tongue, was studied electrophysiologically in the rat chorda tympani nerve. Previous work in electric taste has centered on ON responses to both anodal and cathodal currents. The cathodal OFF response, like ON responses, increased with increasing current intensity until a saturated response level was achieved. Unlike previously reported ON responses, the OFF response did not show a sensitivity to the ionic composition of the fluid bathing the tongue making this the first electrophysiological report of ion insensitivity in electric taste. The cathodal OFF response was sensitive to the duration of the current pulse preceding it. Longer pulses produced larger OFF responses, until with very long pulses (seconds) a saturated response level was achieved. The half maximal response occurred at 12.5 ms. These results have been interpreted to mean that the cathodal OFF response has an origin other than the microvillus membrane, the site most often implied for ON responses, due largely to its ion insensitivity. A probable location may reside with ion channels transversing the basal membrane which are transiently excited at the break of the current resulting in excitation at the receptor-afferent synapse.

Animals↗
PubMed1980

Responses of cortical taste cells and chorda tympani fibers to anodal d.c. stimulation of the tongue in rats.

Single unit activities of the first-order taste neurons (chorda tympani), cortical field potentials and unit responses of cortical taste cells were recorded during anodal D.C. stimulation of the tongue surface in rats. This technique of anodal stimulation was found to be useful for accurate localization of the recording electrode in the cortical taste area, in order to record its unit activities. Salt-and/or cold-sensitive chorda tympani fibers were sensitive exclusively to anodal D.C. stimulation. The relationship between response magnitude and stimulus intensity corresponded approximately to Stevens' power function. In contrast to fibers in the chorda tympani, cortical cold-sensitive cells were less responsive to D.C. stimulation. Moreover, the dominant responsiveness of salt-sensitive cortical cells to D.C. stimulation of the tongue faded away within 1--5 s after onset of the stimulation.

Animals↗
PubMed1982

Physiological characteristics of the solitario-parabrachial relay neurons with tongue afferent inputs in rats.

Among 180 units in the solitary tract nucleus (NTS) of rats, 34 solitario-parabrachial relay neurons (SP neurons), were identified by antidromic activation from the parabrachial nucleus. The SP neurons were classified into two groups, fast and slow, according to their antidromic latencies. The responsiveness of the SP in comparison with non-SP neurons was studied by electrical stimulation of three tongue nerves: the lingual (L), chorda tympani (CT) and glossopharyngeal (G) nerves. About half the SP neurons produced a single spike with an orthodromic latency of 2-5 ms, while about one third of them discharged more than two spikes. A few neurons gave rise to a long-lasting discharge consisting of five or six spikes. Some SP neurons were excited by stimulation of the tongue afferents with a low stimulus intensity, but other SP neurons produced spikes at only very high voltages. Fast SP cells were not differentiated from slow SP cells, except that latency of orthodromic responses to CT stimulation was significantly shorter in the former than in the latter (P less than 0.05, Mann-Whitney U-test). Locations of the SP and non-SP neurons, reconstructed histologically, indicate that they do not distribute evenly throughout the mediolateral extent at the rostral pole of the NTS, but clustered in its medial half.

Afferent Pathways↗
PubMed1992

Influence of tight junctions on the interaction of salts with lingual epithelia: responses of chorda tympani and lingual nerves.

The role of tight junctions in modulating responses from chorda tympani (taste) and lingual (general sensory) nerves are clarified in regard to their responses to salts. Chorda tympani (CT) responses elicited by organic sodium salts require greater Na+ concentrations to elicit the same magnitude of response as NaCl. These data can be understood in terms of the organic anions (compared with Cl-) producing larger liquid-junction potentials across tight junctions between taste cells which, in turn, reduces Na+ influx into taste cells via amiloride-inhibitable channels. The anion contribution to the CT response to different Na+ salts can be eliminated (or enhanced) by voltage clamping the tongue with negative (with respect to the serosal solution) potentials. Whole nerve recordings from the lingual branch of the trigeminal nerve elicited by NaCl (and other salts) were reversibly inhibited by the tight junction blocker, LaCl3. These data suggest that small hydrophilic molecules elicit responses from trigeminal fibers by diffusing across tight junctions between epithelial cells and altering the composition of the extracellular space.

Amiloride↗
PubMed1993

Ultrastructure of the taste disc in the red-bellied toad Bombina orientalis (Discoglossidae, Salientia).

The taste disc of the red-bellied toad Bombina orientalis (Discoglossidae) has been investigated by light and electron microscopy and compared with that of Rana pipiens (Ranidae). Unlike the frog, B. orientalis possesses a disc-shaped tongue that cannot be ejected for capture of prey. The taste discs are located on the top of fungiform papillae. They are smaller than those in Ranidae, and are not surrounded by a ring of ciliated cells. Ultrastructurally, five types of cells can be identified (mucus cells, wing cells, sensory cells, and both Merkel cell-like basal cells and undifferentiated basal cells). Mucus cells are the main secretory cells of the taste disc and occupy most of the surface area. Their basal processes do not synapse on nerve fibers. Wing cells have sheet-like apical processes and envelop the mucus cells. They contain lysosomes and multivesicular bodies. Two types of sensory cells reach the surface of the taste disc; apically, they are distinguished by either a brush-like arrangement of microvilli or a rod-like protrusion. They are invaginated into lateral folds of mucus cells and wing cells. In contrast to the situation in R. pipiens, sensory cells of B. orientalis do not contain dark secretory granules in the perinuclear region. Synaptic connections occur between sensory cells (presynaptic sites) and nerve fibers. Merkel cell-like basal cells do not synapse onto sensory cells, but synapse-like connections exist between Merkel cell-like basal cells (presynaptic site) and nerve fibers.

Animals↗
PubMed1994

Differential distribution of two Ca(2+)-dependent and -independent K+ channels throughout receptive and basolateral membranes of bullfrog taste cells.

We could identify two types of K+ channels, of 80 and 40 pS conductance, respectively, in the bullfrog taste cell membrane using excised and cell-attached configurations of the patch-clamp technique. The taste cell membrane could be divided into four membrane parts--receptive area, apical process, cell body and proximal process. The 80-pS K+ channels were dependent on voltage and Ca2+ and were located exclusively on the receptive membrane and the apical process membrane. The 40-pS K+ channels were independent of voltage and Ca2+. The open probability of 40-pS K+ channels was decreased by the simultaneous presence of cyclic adenosine monophosphate (cAMP) and adenosine triphosphate (ATP), and the suppressive effect was antagonized by protein kinase inhibitor (PKI). Although 40-pS K+ channels were found in a high density on the receptive and apical process membranes, the channels also were present in the other two parts of the taste cell membrane. These results suggest that the two different types of K+ channel in the bullfrog taste cells may play different roles in gustatory transduction.

Adenosine Triphosphate↗
PubMed1975

[New morphologic principles of the physiology of smell and taste].

New results as revealed by scanning and transmission electron microscopy have given us further knowledge about the structure of the olfactory region of vertebrates. With comparative studies we are now able to discuss the functional relationship of this region. In all vertebrates the olfactory cell is a primary sensory cell. The apical segment of the olfactory cell with its olfactory vesicle is involved in the formation of the olfactory border. As a rule of the receptor possesses cilia or cilia-like processes. These are absent in the olfactory receptor of the shark, the microvillus receptor of the fish and the olfactory cell of Jabonsons organ of amphibians, reptiles and mammals. The odorous substances in the fish are brought to the receptor membrane by the water flow. In air breathing vertebrates a terminal film is present. This film is a product of secretion from the Bowmans glands. Gasous odorous substances must first be dissolved in the terminal film and penetrate it before reaching the receptor membrane. The cilia-like olfactory process of the fish in the proximal segment is not essentially different from the kinocilia of the supporting cell, except that they are shorter. In contrast the olfactory cell of air-breathing vertebrates form cilia-like processes with a short cilia-like proximal segment and a long and very thin distal end piece. In the amphibians and sauropsidians the end pieces can have a length of up to 150 mu and up to 80 mu in mammals. The olfactory vesicles with its processes undergo continuous regeneration. The olfactory epithelium of man show the same structural formation as observed in other mammals. Regressive changes in the adult can lead to a reduction in the number of sensory cells and also to a flattening of the epithelium. Morphological criteria for regenerative processes in the sensory cell structures are present. A specialized olfactory cell type has been found in some teleosts. This cell is characterized by a small pit below the olfactory border in which the cilia of the olfactory cell are redrawn. There is some evidence that this olfactory cell type may be compared with the olfactory cells in the parafollicular tubes of lamprey. The so called rod-shaped receptor in the olfactory mucosa of fishes has no axon and is therefore no olfactory cell. The same kind of cell is also present in the olfactory mucosa of air-breathing animals. We classify this cell as brush cell.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1980

A fluorescence histochemical study of the monoamine-containing cell in the developing frog taste organ.

Sequential changes in the monoamine-containing cell (MC cell) of the developing frog tongue has been studied by fluorescence histochemistry using uptake of 5,6-dihydroxytryptamine. At st. 16, a few yellow fluorescent cells, here called MC cells, appeared in random order at the uppermost layer of the dorsal epithelium. They were round or elliptical in shape. At st. 18 the MC cells, greatly transformed, were found at the periphery of the sensory disc primordium which first appears during this stage. The MC cell was made up of three parts: perikaryon, process and terminal portion. The perikaryon was located at the upper half of the epithelium and from it a single process stretched vertically toward the basal lamina, above which the dilated terminal portion was found. Thereafter the perikaryon gradually moved toward the basal layer while remaining at the periphery of the disc primordium. Meanwhile the terminal portion moved over the basal lamina toward the center of the disc primordium. At st. 22, the whole of the MC cell lay flat above the basal lamina. The perikaryon was localized at the periphery of the sensory disc and from there the process stretched toward the center. Thus, the morphology of MC cells resembled the adult state, except for smaller size. MC cells were never observed in the subepithelial connective tissue in the present study. This seems to suggest that the MC cell of the frog fungiform papilla is of epithelial origin.

5,6-Dihydroxytryptamine↗
PubMed1975

Specific effect of 5,6-dihydroxytryptamine on the monoamine fluorophore of the frog's gustatory cells.

A specific formaldehyde-induced yellow fluorescence, suggesting the presence of serotonin-like monoamine has been demonstrated in the gustatory cells of the frog. The fungiform papillae of frogs were examined fluorescence-histochemically after intraperitoneal injection of 5,6-dihydroxytryptamine. The results indicated that the fluorophore of gustatory cells was affected selectively by the drug injection: the yellow fluorescence was transiently enhanced 3 hours after the drug injection, thereafter being reduced rapidly. The effect of 5,6-dihydroxytryptamine was long-lasting with the reduction of the yellow fluorophore persisting at least for the experimental duration of 14 days. A single injection of 6-hydroxydopamine induced a complete depletion of noradrenaline fluorescence from adrenergic nerve terminals, while the fluorescence of gustatory cells was not affected by a high dose of the drug. The present results with pharmacologic treatments further support the view that the gustatory cell of the frog contains a serotonin-like monoamine.

5,6-Dihydroxytryptamine↗
PubMed1976

Taste qualities elicited by electric stimulation of single human tongue papillae.

Single human taste papillae in 5 young test subjects were electrically stimulated 84 times each with a silver wire (0.4 mm tip diameter) versus a 5 x 3.5 cm2 reference electrode on the left wrist of the subject. The electrical pulses were positive (54 papillae) or negative (45 papillae) of 0.5 msec duration and had a frequency of 50, 100, 200, 400, 600 or 800 Hertz. For control 45 papillae were merely touched by the electrode without current stimulation. Significant gustatory and tactile results (x2-test, P less than or equal to 0.05) signaled by the subjects were: a) on anodic stimulation 50 +/- 5% of the touched papillae gave overall taste responses, namely 22.2% sour, 3.8% bitter and 1.8% salty; the rest were mixed sensations. Sweet was not reported in these final experiments; b) on cathodic stimulation 42.2 +/- 5% of the papillae responded with taste, which again were reported as 22.2% sour, 2.2% salty, the rest mixed; c) on mere touching there were hardly any gustatory sensations reported. - These results indicate only a relative specifity for each single human taste papilla and its taste fibres.

Adolescent↗