BROAD TUNING OF RAT TASTE CELLS FOR 4 BASIC TASTE STIMULI

The breadth of responsiveness of rat taste cells to the four basic tas te stimuli was studied using the entropy measure (H) proposed by Smith and Travers. H values range from 0.0 for narrow tuning to 1.0 for bro ad tuning. Based on the responses of depolarizing receptor potentials of 26 rat taste cells to the four basic taste stimuli, taste cells wer e classified into nine NaCl-best, four Q-HCl (quinine-HCl)-best, 10 HC l-best and three sucrose-best cells. NaCl-best cells were narrowly tun ed to the four basic taste stimuli, but the other three stimuli-best c ells were broadly tuned to the stimuli. In all, 85% of the taste cells responded to more than one of four basic taste stimuli. The mean H va lues for NaCl-best, Q-HCl-best, HCl-best and sucrose-best cells were 0 .285, 0.832, 0.781 and 0.796 respectively. The mean H value for all 26 taste cells was 0.621. This was larger than H in rat gustatory fibers . Transformation of large H values in taste cells into small H values in taste fibers may be due to a non-random interaction between taste c ells and taste fibers during the synaptic formation. Broad tuning prop erties of rat taste cells suggest that the across-taste cell response pattern may play an important role in taste quality coding mechanisms.