FUNCTIONAL PLASTICITY OF REGENERATED AND INTACT TASTE RECEPTORS IN ADULT-RATS UNMASKED BY DIETARY-SODIUM RESTRICTION

Unilateral chorda tympani nerve sectioning was combined with instituti on of a sodium-restricted diet in adult rats to determine the role tha t environment has on the functional properties of regenerating taste r eceptor cells. Rats receiving chorda tympani sectioning but no dietary manipulation (cut controls) and rats receiving only the dietary manip ulation (diet controls) had normal responses to a concentration series of NaCl, sodium acetate (NaAc), and NH4Cl. However, responses from th e regenerated nerve in NaCl-restricted rats (40-120 d postsectioning) to NaCl and NaAc were reduced by as much as 30% compared to controls, indicating that regenerating taste receptors are influenced by environ mental (dietary) factors. Responses to NH4Cl were normal; therefore, t he effect appears specific to sodium salts. Surprisingly, in the same rats, NaCl responses from the contralateral, intact chorda tympani wer e up to 40% greater than controls. Thus, in the:same rat, there was ov er a twofold difference in sodium responses between the right and left chorda tympani nerves. A study of the time course of the functional a lterations in the intact nerve revealed that responses to NaCl were ex tremely low immediately following sectioning (about 20% of the normal response), and then increased monotonically during the following 50 d until relative response magnitudes became supersensitive. This functio n occurred even when the cut chorda tympani was prevented from reinner vating lingual epithelia, demonstrating that events related to regener ation do not play a role in the functional properties of the contralat eral side of the tongue. The anomalies in responses in the regenerated and the uncut nerves are attributable to functional alterations in th e sodium transducer, the amiloride-sensitive sodium channel. Specifica lly, sodium transduction via the channel is decreased or increased fro m normal levels, depending on the experimental conditions. Although ef ferent neural effects cannot be disregarded, the present results sugge st that alterations in circulating factors may modulate response prope rties of intact, lingual taste receptor cells.