Effects of menthol on peripheral nerve and cortical unit responses to thermal stimulation of the oral cavity in the rat.

Neurophysiological responses were recorded in individual fibers of the lingual and chorda tympani nerves and in single cortical neurons in the rat in response to a battery of tactile, thermal and chemical stimuli applied to the oral cavity. Two categories of thermally sensitive units were identified. Chorda tympani fibers and one type of cortical unit ('Type I') were activated by cold water stimulation but were unaffected by warm water or menthol. In contrast, lingual fibers and a different category of cortical units ('Type II') were extremely sensitive to menthol exposure. These units were cold water sensitive, however, this sensitivity was suppressed following menthol presentation.