RESPONSES OF SINGLE LINGUAL NERVE-FIBERS TO THERMAL AND CHEMICAL-STIMULATION

The goals of this study were to characterize the responses of: (1) the rmally-sensitive fibers of the lingual branch of the trigeminal nerve to cooling from 35 degrees to 10 degrees C at a rate of 1 degrees C/s; and (2) these neurons to a mid-range concentration of NaCl (150 mM), glucose (150 mM), citric acid (0.3 mM), and quinine-HCl (3 mM) at 35 d egrees and 25 degrees C. A cluster analysis of 47 neurons' responses t o cooling revealed two major groups and one minor group. Group 1 neuro ns (n = 19) had a shorter latency, exhibited faster time-to-peak activ ity, and responded over a smaller range of temperature compared to Gro up 2 neurons (n = 22). Group 3 neurons (n = 6) exhibited the longest r esponse latency and responded over a wider cooler range of temperature . Twenty-five out of thirty-one thermally-sensitive, non-tactile lingu al neurons responded weakly to at least one chemical stimulus, with so me neurons responding to 2, 3, or all 4 chemical stimuli. Group 1 neur ons responded to more chemical stimuli at 35 degrees C, while Group 2 neurons responded more at 25 degrees C. Under their optimal temperatur e conditions, Group 1 and Group 2 neurons responded most often to citr ic acid and least often to glucose, with NaCl and Q-HCl eliciting an i ntermediate number of responses. As a whole, the responses of thermall y-sensitive fibers to chemical stimulation were modest at best with an absence of chemical specificity. There was no evidence of a 'best' st imulus, although there was a suggestion of temporal coding. (C) 1998 E lsevier Science B.V.