SALT PREFERENCE: INFLUENCE OF AGE AND STRAIN

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The long range goal of this project is to identify factors which contribute to variations in salt preference and intake. Salt preference refers to the ingestion of sodium or sodium chloride (NaCl) in the absence of physiological need and is of particular Interest because high salt Intake has been Implicated In the development and maintenance of essential hypertension in humans. Previous work in our laboratory has defined situations in which rats show significant departures from the "species typical norm" of salt preference. Two rat models have been examined where salt preference deviates sharply from this norm. One --the Infant rat- - could be characterized as a salt glutton, since it does not avoid hypertonic NaCl solutions at concentrations as high as 4% and 6%, which would be totally avoided by adult rats. The other --an inbred strain known as the Fischer-344 rat-- displays an unusual distaste for NaCl solutions. Adult Fischer-344 rats fall to prefer even isotonic or hypotonic NaCl solutions to water. These behaviors are at the extremes on a continuum of salt preference. Although a number of factors are likely to be involved, a focus of this proposal is the hypothesis that age and strain differences in amiloride-sensitive sodium transport at the tests bud contribute to the wide variations in NaCl preference displayed by these rats. Behavioral studies of taste preference in short and long term tests will be utilized to characterize the salt aversion displayed by Fischer-344 rats as well as examine its ontogeny. The ingestive behavior displayed by 10-day-old Long Evans rats toward salts will also be examined. Behavioral and electrophysiological approaches will be utilized to assess the hypothesis that strain and age differences in amiloride-sensitive sodium transport mechanisms at the taste bud are involved both in the aversion to salt displayed by Fischer-344 rats and in the emergence of avoidance of hypertonic NaCl solutions during the suckling period Behavioral studies of amiloride sensitivity delivery amiloride and measure licking behavior to NaCl solutions in brief access tests with a lickometer, electrophysiological studies examine multiunit activity of the chorda tympani nerve to NaCl solutions after water or amiloride pretreatment.