Hyperinnervation Produces Inhibitory Interactions between Two Taste Nerves"

Several researchers have presented evidence that suggests that the processing of gus-tatory information at the level of the taste bud can involve interactions among taste fibers, for example, Bernard ' and Miller. ' We report here that two chorda tympani nerves in the same peripheral field may interact to inhibit gustatory impulse traffic to the brain. METHODS The proximal portion of the right chorda-lingual nerve was sutured to the distal stump of the left lingual nerve in 44 mongolian gerbils. Nine to fifteen months after the initial surgery, a second operation was performed on six gerbils. The native chorda tympani was removed in four gerbils and the foreign chorda tympani was removed in two. In 10 control animals the left lingual nerve and the right chorda-lingual nerve were transected. The latter was reconnected with an 11-0 suture to allow reinnervation of the right side of the tongue. Five to twenty months after the initial surgery, the chorda tympani nerves were exposed in the left and right middle ears and impulse activity simultaneously recorded from the two nerves while stimulating the tongue with a variety of taste solutions. It was also possible to electrically stimulate one chorda tympani while simultaneously recording from the other. Each animal was sacrificed at the end of the recording session. The tongue was removed and processed for light microscopy. Fungiform taste buds were counted and their positions on the tongue noted. A subset of taste buds was analyzed morphometrically. Counts of taste cells were made from plastic sections of fungiform taste buds from three experimental and four normal animals