Inhibitory interactions among rodent taste axons.

The left side of the tongue of the Mongolian gerbil, Meriones unguiculatus, was experimentally innervated with both chorda tympani nerves. While this dual innervation did not increase the number or volume of fungiform taste buds on the left side, at least half of the taste buds were dually innervated since they could be neurotrophically maintained by either chorda tympani nerve. Impulse discharges occurred simultaneously in the native (left) and foreign (right) chorda tympani nerves when the taste stimulus was restricted to the left side of the tongue. The marked attenuation of the phasic or tonic portions of some taste responses suggested that dual innervation had enhanced inhibition, especially of foreign chorda tympani responses. This was confirmed when electrical stimulation of the native chorda tympani reduced the peak summated action potential discharges of the foreign chorda tympani to NaCl or sucrose by an average of 52 and 41%, respectively. Inhibition began within seconds and continued with an 11.5-min half-life. The inhibition was unaffected by acutely disconnecting either chorda tympani nerve from the brain. We propose that dual chorda tympani innervation accentuated lateral inhibitory connections that may function normally to reduce spurious sensory signals in taste axons.