Gustatory responsiveness of chorda tympani fibers in the cynomolgus monkey

Responses of chorda tympani (CT) fibers of cynomolgus monkeys to various gustatory stimuli were analysed to obtain quantitative data on their response properties and to reveal the coding of gustatory information. Based on responses of 66 fibers to the four basic gustatory stimuli, they were classified into 16 sucrose-best, 28 NaCl-best, 11 HCl-best and 11 QHCl (quinine hydrochloride)-best fibers. Sucrose-best fibers were narrowly tuned to sucrose, while HCl-best fibers were broadly tuned to the four stimuli. The average breadth of response measure. H for all the 66 fibers was 0.375. The average value of H for sucrose-, NaCl-, HCl- and QHCl-best fibers was 0.276, 0.348, 0.634 and 0.384, respectively. Hierarchical cluster analysis performed on responses of 25 fibers to 14 gustatory stimuli revealed that all the stimuli except for 0.3 M Na-saccharin were grouped into four clusters; sucrose and 0.01 M Na-saccharin, NaCl and LiCl, acids, and non-sodium and -lithium salts, and QHCl. It is concluded that in the monkey CT each of the four classes of fibers predominantly contributes to mediate gustatory information for sweet, salty, sour and bitter stimuli.