Gustatory impulse discharges in response to saccharin in rats and hamsters

1. Impulse discharges produced by saccharin sodium as well as four basic gustatory stimuli were recorded in chorda tympani fibres of rats and hamsters.2. Units predominantly sensitive to NaCl showed a concentration-response magnitude curve for saccharin sodium similar in shape to that for NaCl but smaller in magnitude. Units of this category did not respond to 0.01 M saccharin buffered with tris(hydroxymethyl)aminomethane. Response to saccharin sodium in these units are considered to result from stimulation of receptor molecules by Na ions.3. Units predominantly sensitive to sucrose showed a concentration-response magnitude curve for saccharin sodium with a maximum magnitude at about 0.01-0.1 M. Impulse discharges produced by sucrose and saccharin sodium showed rhythmic burst-like firing. Units of this category responded well to 0.01 M saccharin. Responses to saccharin sodium in these units are attributed to the reaction between saccharin molecules and receptor sites.4. The optimum concentration at which a greatest response magnitude was found varies from one unit to the other and is inversely related to sucrose sensitivity, units highly sensitive to sucrose showing a low optimal concentration. Presence of the optimum concentration is explained by a mechanism known as the non-competitive auto-inhibition.5. Off-responses were observed in units predominantly sensitive to sucrose when 0.03-1 M saccharin sodium applied to the tongue was rinsed with water.6. Neural information for saccharin sodium is described quantitatively in relation to that for four basic gustatory stimuli.

Multiple sensitivity of chordat typani fibres of the rat and hamster to gustatory and thermal stimuli

1. Impulse discharges in single chorda tympani fibres of rats and hamsters in response to gustatory stimuli representing the four basic qualities of taste as well as to cooling and warming of the tongue were recorded.2. In both rats and hamsters many fibres responded to more than one kind of gustatory stimulus as well as to thermal ones. The thermal sensitivity of these fibres was found to be about -0.5 impulses/sec. degrees C for cooling and 0.5 impulses/sec. degrees C for warming.3. Statistical calculations of the frequency of responses of chorda tympani fibres to single gustatory stimuli or combinations of stimuli were made, assuming that responsiveness to any one stimulus is independent of that to other stimuli. Evidence for relatively specific sensitivity to a particular stimulus or a particular combination of stimuli was obtained in the rat and the hamster.4. Across-fibre correlation coefficients between the amounts of responses to a pair of stimuli were calculated. In both the rat and the hamster, significant positive correlations were obtained with HCl, quinine and cooling. In addition, a positive correlation between sucrose and warming and a negative correlation between sucrose and NaCl were obtained in the hamster. The results are discussed in relation to the interaction of gustatory and thermal sensations of the human tongue.