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.