Salt preference in the preweaning rat

Salt (NaCl) preference of 5-20-day-old rats was examined using a method which elicits independent ingestive responses. Rats were placed in a warm, moist incubator on toweling which was saturated with water or test solutions. Active mouthing responses were seen which were directed toward the towel soaked with solution and weight gain in a 25-min test was taken as an index of ingestion. At most ages pups preferred hypertonic saline solutions to water and at 10 days of age rats appeared particularly insensitive to the aversiveness of concentrated (4-8%) NaCl solutions. In contrast to the 10-, 15-, and 20-day-old rats, the 5-day-old rats never preferred NaCl solutions to water and avoided them at concentrations which older rats preferred. This pattern of NaCl preference cannot easily be explained in terms of the known increases in sensitivity of the rat's taste system to NaCl stimulation with age. Ingestion of NH4Cl solutions was also examined and at 10 days of age significant preference for concentrated NH4Cl solutions was evident which contrasts markedly with the behavior of older pups and adult rats when presented with NH4Cl solutions. The relationship between the present findings and available electrophysiological data from the chorda tympani and nucleus of the solitary tract are discussed.