The time course of solitary nucleus gustatory responses: Influence of stimulus and site of application

The responses of 64 neurons in the nucleus of the solitary tract (NST) of the rat were recorded while independently stimulating the anterior tongue (AT) and the nasoincisor ducts (NID) with sucrose and NaCl. The time course of this activity has been analyzed by averaging the responses (500 ms bins) to each stimulus:receptor subpopulation combination across neurons. Regardless of the site of stimulus application, the average time course of the NaCl responses was similar: both peaked rapidly (1.0-1.5 s), with a peak/tonic ratio of >2:1. On the other hand, when the AT or NID was stimulated with sucrose, the average time course of the responses varied. The mean sucrose:NID response rose rapidly (1.0-1.5 s) to its maximum, which was 2.Ox the magnitude of the tonic response. Sucrose on the anterior tongue elicited a response with a time course that differed from all other responses studied: it peaked slowly (3.5-4.0 s), and exhibited a peak/tonic ratio of only 1.5:1. In distinction to what had been observed for peripheral fibers, a finer-grained analysis of individual NST responses evoked by stimulating the AT and NID with sucrose revealed minimal evidence for regular bursting.