SODIUM-DEFICIENT DIET REDUCES GUSTATORY ACTIVITY IN THE NUCLEUS OF THE SOLITARY TRACT OF BEHAVING RATS

The activity of single taste neurons was recorded from the nucleus of the solitary tract before (n = 41) and after (n = 58) awake, behaving rats were switched to a sodium-free diet. During sodium deprivation, t he spontaneous activity of the neurons increased (142%), but responses to water and sapid stimuli decreased. For all neurons in the sample, the mean response to water decreased to 72% of its predeprivation leve l, NaCl dropped to 53%, sucrose to 41%, citric acid to 68%, and quinin e HCl to 84%. Despite the drop in magnitude, the response profiles of the taste neurons were not changed by the dietary condition. In the Na -replete state, 61% of the activity elicited by NaCl occurred in NaCl- best cells and 33% in sucrose-best neurons. In the depleted state, the se values were 60 and 26%, respectively. Nevertheless, at the highest concentrations tested, deprivation did alter the relative responsivene ss of the gustatory neurons to sucrose and NaCl in specific categories of neurons. Compared with acute preparations, dietary sodium deprivat ion in awake, behaving rats produced a more general reduction in the g ustatory responses of neurons in the nucleus of the solitary tract. Th e largest reductions in elicited activity occurred for the ''best stim ulus'' of a particular neuron, thus leading to smaller differences in response magnitude across stimuli, particularly at the highest concent rations tested.