High dietary sodium enhances gustatory nerve activity and behavioral responses to NaCl

Neural and behavioral taste responses to NaCl were studied in rats receiving a high-salt diet. Salt preferences and voluntary sodium intake were measured by the 24-h two-bottle choice method over a wide concentration range of NaCl solutions. As expected, the salt-loaded rats showed lower preference responses for all the solutions tested, which were presented in ascending order from 0.001 to 1.0 M NaCl. However, they freely ingested significantly greater amounts of sodium than the controls by drinking larger volumes of saline solution throughout the hypotonic concentration range, from 0.001 to 0.1 M NaCl. They showed lower voluntary intake of sodium only for isotonic and hypertonic solutions. Electrophysiological recordings from the chorda tympani nerve showed that the taste responses of the salt-loaded rats were greater in magnitude than those of the controls, and the neural stimulus-response function of the experimental group had a significantly steeper slope but no apparent difference in threshold. These experiments indicate that salt-loaded rats have enhanced appetitive responses to NaCl that may be mediated by increased sensory input.