NaCl concentration alters temporal patterns of drinking and eating by rats

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Abstract
To obtain an understanding of the role of taste in NaCl preference-aversion under standard laboratory feeding conditions, we characterized the eating and drinking patterns of rats maintained on powdered food, water, and NaCl solution. The concentration of NaCl was varied systematically from 0.01 to 0.4 M with a single concentration present for four consecutive days. In addition to daily intake, the number and duration of ingestion bouts, and the number of switches between food and fluid and between water and saline were recorded throughout the day/night cycle. The availability of NaCl solution did not alter the typical pattern of night-time feeding and prandial (drinking after a meal) drinking. As shown previously, NaCl intake was highest for 0.15 M NaCl and declined at both stronger and weaker concentrations. Variations in drinking bout number and duration determined amount consumed. Drinking bout duration was highest for 0.2 M NaCl then declining progressively at both stronger and weaker concentrations. The number of drinking bouts was highest for 0.04 M NaCl, a concentration slightly above the adapting salivary sodium concentration, declining linearly thereafter with stronger NaCl concentrations. The availability of NaCl solution influenced the amount of food consumed, as well as the number and duration of food bouts. Food bout number was highest in the presence of the weakest 0.01 M NaCl solution, while food bout duration was highest in the presence of hypertonic NaCl concentrations. Most switching behavior occurred between meal consumption and drinking and little between drinking fluids. When 0.01–0.08 NaCl solutions were available, the rats drank saline after a meal; when hypertonic 0.3–0.4 M NaCl solutions were available, they drank water after a meal. In the presence of intermediate NaCl concentrations (0.15–0.20), the choice of fluid consumed after a meal was more equivocal to the extent that there was increased switching between water and saline and vice versa. The significance of these differences in the micromolar features of eating and drinking are discussed in relationship to taste and postingestional control mechanisms of ingestion.