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D V Smith

Publications and source records attributed to D V Smith.

At least 73 records · Page 4Linked to original sources
PubMed1984

Responsiveness of neurons in the hamster parabrachial nuclei to taste mixtures.

Responses from hamster parabrachial nuclei neurons to stimulation of the anterior tongue with sucrose, NaCl, HCl, quinine hydrochloride, and the six two-component mixtures of these stimuli were recorded. A cell's response to a mixture approached its response to the mixture's more effective component in the majority of cases, but was sometimes greater or smaller than this response. The best predictor of a neuron's response to a mixture, then, was its response to the mixture's more effective component. The single-component stimulus producing the maximum response was determined for each neuron and the response to this stimulus was compared with the responses evoked by the six mixtures. For 30% of the cells, a mixture elicited a response reliably, but only 1.1-2.1 times greater than the response to the best single-component stimulus. Thus, there were no neurons specialized to respond to these mixtures. The across-neuron patterns elicited by mixtures and the responses of best-stimulus classes to mixtures were studied for comparison with psychophysical data on taste mixtures. Mixtures were usually correlated with single-component stimuli in the mixture, but not with stimuli not in the mixture. In fact, five of the six mixtures fell directly between their components in a multidimensional scaling plot. In addition, a mixture was most effective in stimulating only those classes of neurons maximally stimulated by the mixture's components. These results correlate with psychophysical data suggesting that mixtures of taste stimuli evoke the same taste qualities as evoked by the mixture's components.

Action Potentials↗
PubMed1983

Gustatory neuron types in hamster brain stem.

In general, mammalian taste neurons are broadly responsive to stimuli representing different taste qualities. In the hamster, this breadth of tuning increases systematically from peripheral to successively higher brain stem neurons. Some investigators have classified taste-responsive neurons into "best-stimulus" categories on the basis of which of the four basic stimuli (sucrose, NaCl, HCl, or quinine hydrochloride) elicits the maximum response. However, attempts by others to demonstrate the existence of taste neuron types in the chorda tympani nerve and medulla of the rat using hierarchical cluster analysis have not been successful, resulting in the conclusion that there are no neuron types in the rat gustatory system. The present study was designed to look at the question of neuron types in the hamster, a species with a broader range of gustatory sensitivities to anterior tongue stimulation. Responses of 30 neurons in the nucleus tractus solitarius (NTS) and 31 neurons in the parabrachial nuclei (PbN) of the hamster to an array of 18 stimulus compounds were recorded extracellularly. The similarities of the neural response profiles of these cells at each synaptic level were compared using multivariate statistical techniques. The possiblee grouping of cells on the basis of similarities in their response functions was examined with hierarchical cluster analysis, and the relationships among these response functions were examined with multidimensional scaling. The results of the cluster analysis suggested that at both the NTS and PbN, there are three clusters of neural response profiles. These three clusters of response profiles are characterized at both synaptic levels by their predominant sensitivity to 1) sucrose and other sweet-tasting compounds, 2) sodium salts, and 3) nonsodium salts and acids. Representation of these neurons in a two-dimensional space yielded three nonoverlapping groups of cells in both the NTS and PbN, corresponding to the three groups identified by the hierarchical cluster solution. Classification of taste neurons either by their best stimulus or by other criteria has been criticized on the grounds that it may constitute an arbitrary division of a continuous population of neurons. The techniques of numerical taxonomy, which take the cells' variability into account, also result in a grouping of taste cells into classes. These taxonomic classes agree in most instances (80% in NTS and 80.6% in PbN) to a best-stimulus classification. The failure of some investigators to find types of neural response profiles in the rat gustatory system may be the result of species differences in taste sensitivity as well as differences in the statistical procedures employed.

Acids↗
PubMed1976

Recovery of excitability after gustatory adaptation: effects of stimulus intensity.

The excitability of the rat chorda tympani nerve following adaptation to NaCl was measured by observing the recovery of the transient portion of the integrated neural response. When a single concentration of NaCl was used as a test stimulus, recovery time was positively correlated with the concentration of the adapting solution, a relationship common to a number of other sensory systems. Adapting and testing with the same concentration of NaCl produced very little relationship between concentration and recovery time. It is suggested that the relativley extensive period of postexcitatory depression is due to a prolonged inaccessability of tast receptor sites that results in a reduction in the rate of stimulus-receptor interaction.

Adaptation, Physiological↗
PubMed1975

Multiple sensitivity to chemical stimuli in single human taste papillae.

The sensitivities of 15 human fungiform papillae were tested using a 5-alternative forced-choice procedure. Subjects were aked to recognize which of the following stimuli was presented to a papilla on each of 250 trials: 5.0 M NaCl, 0.5 N citric acid, 1.0 M quinine hydrochloride, and distilled H2O. Solution droplets were delivered to individual papillae from 0.5 mm diameter platinum wire loops. Based on each subject's responses to distilled H2O, corrections were made for individual response biases. Of the papillae tested, 33 percent responded to all four compounds, 33 percent to three, none to only two, 20 percent to only one, and 13 percent to none of the chemical stimuli. These results are contradictory to earlier work, in which it was suggested that taste quality is encoded by chemically specific papillae, but are consistent with the electrophysiological data suggesting multiple sensitivity of mammalian gustatory receptor cells and first-order neurons. The data suggested that the narrow range of sensitivity reported by von Békésy [2] was determined by the reciprocal relationship between the size of the stimulated area and the concentration necessary to elicit a threshold sensation.

Adolescent↗
PubMed1975

Sensitivity of the rat gustatory system to the rate of stimulus onset.

Responses of the rat chorda tympani nerve were obtained to stimulation of the tongue with both linearly rising anodal current of varying intensity and rate of rise and NaCl presented at different concentrations and rates of flow. The amplitude of the transient portion of the integrated chorda tympani response was a power function of the rate of current rise. The duration of the transient response paralleled the rising phase of the current and the neural response fell to a tonic level proportional to current intensity when the rising current reached its plateau. Anodal currents of different final intensities but presented at the same rate of rise produced transient responses of the same amplitude. Responses of single chorda tympani fibers exhibited the same phasic and tonic components that were characteristic of the whole nerve. When NaCl was presented to the tongue at different rates of flow, the chorda tympani response reflected a sensitivity to stimulus onset rate paralleling that shown to linearly rising current.

Animals↗
PubMed1975

An analysis of the time course of gustatory neural adaptation in the rat.

Neural responses were recorded from the rat chorda tympani nerve following stimulation of the tongue with several concentrations of NaCl. These responses were integrated using a fast time constant (47 ms), and the time course of the decline in neural discharge from the peak of the transient response was computer analyzed. The time course of the adaptation process was described by a constant term and two exponentially decaying components, which most likely reflect the existence of two separate mechanisms contributing to the adaptation process in taste. The constant term and the amplitude of the second gradual exponential decay were correlated with NaCl concentration, whereas the amplitude of the initial rapidly declining exponential component was independent of stimulus intensity. The initial transient response of the chorda tympani nerve may be a function of the rate of stimulus adsorption, whereas the gradual second decline in the neural response may reflect an adaptive mechanism of the taste receptor cell.

Adaptation, Physiological↗