TASTE IN CHIMPANZEES .2. SINGLE CHORDA TYMPANI FIBERS

Data are presented from 48 taste fibers in chorda tympani nerves of 10 chimpanzees during taste stimulation with 29 stimuli. The results dem onstrated a higher taste fiber specificity than in any other mammalian species reported; breadth of tuning equals 0.3. Hierarchical cluster analysis separated an S-cluster (50% of all fibers), an N-cluster (31% ), and a Q-cluster (19%). The S-cluster showed the highest specificity . Its fibers responded, with few exceptions, to every sweetener tested , including the sweet proteins brazzein and monellin. The response gre w with increasing sweetener concentration. A large response to one swe etener was generally accompanied by a large response to all other swee teners, and vice versa. Except for one broadly tuned fiber, the fibers of the S-cluster never responded to the bitter compounds. The fibers of the Q-cluster were more broadly tuned than any other fibers. Quinin e hydrochloride was their best stimulus, but most fibers were also sti mulated by KCl and NaCl with amiloride. Acids stimulated some of these fibers. The N-cluster could be divided into 3 subclusters: an Na-subc luster (3 fibers), Na-K subcluster (10 fibers), and M-subcluster (3 fi bers). The Na-fibers responded strongly to, and were quite specific to , NaCl and LiCl stimulation but not to KCl, and fibers of the Na-K sub cluster responded equally well to NaCl and KCl. The response to NaCl w as suppressed by amiloride in the fibers of the Na-subcluster, but not in the fibers of the Na-K subcluster. Umami compounds elicited the st rongest responses in the M-subcluster. (C) 1997 Elsevier Science Inc.