EFFECTS OF SODIUM DEPLETION ON COMPETITION AND SUMMATION BETWEEN REWARDING EFFECTS OF SALT AND LATERAL HYPOTHALAMIC-STIMULATION IN THE RAT

The effect of sodium depletion on the value of lateral hypothalamic (L H) stimulation and on competition and summation between saline reward and LH reward was assessed. Sodium depletion did not alter curves rela ting the number of LH rewards earned per trial to the number of stimul ation pulses per train, suggesting that negative sodium balance does n ot alter the reward value of the stimulation. In contrast, sodium depl etion increased the ability of saline (0.9% NaCl) to compete with LH s timulation in a forced-choice preference test. Summation between the e ffects of the 2 rewards was also seen under sodium depletion. These fi ndings imply that the rewarding effects of saline and LH stimulation a re evaluated within a common system of measurement and that negative s odium balance modulates the value of the saline reward upstream from t he point where the rewarding effects of saline and LH stimulation are combined.