Thirst‐induced anorexias and the ontogeny of thirst in the rat

Abstract

In previous work (Leshem, M., Boggan, B., and Epstein, A.N. (1988). The ontogeny of drinking evoked by activation of brain angiotensin in the rat pup. Dev. Psychobiol. Vol.21, pp. 63-75) we showed that thirst elicited by activation of the brain's renin-angiotensin system in the suckling becomes specific to water after 16 days of age. However, in the suckling, we did not find the anorexia that reportedly accompanies angiotensin-induced thirst in the adult. This suggests the existence of a further stage in the ontogeny of thirst. Therefore, the present study pursued the ontogeny of thirst and its effects on milk intake through prepubescence into adulthood. Experiment 1 revealed that intracranial renin does not cause an anorexia to milk in prepubescent or adult rats. Experiment 2 showed that the absence of anorexia is true of thirst induced by renin but not by cellular dehydration, although both dipsogens suppressed milk intake when rats also had water available. Experiment 3 confirmed that the preweanling shows anorexia to solid food, as does the adult. Together with other work, these findings suggest that the ontogeny of the thirsts aroused by renin or intracellular dehydration is complete before weaning.

Exercise Increases the Preference for Salt in Humans

“…Thus salt hunger can be dissociated from other taste preferences, as thirst and hunger are dissociated in thirst-induced anorexia (Leshem & Epstein, 1988).…”

Effects of physiological state on oral habituation in developing rats: Cellular and extracellular dehydration

“…However, by 12 days of age, the effects of cellular and extracellular dehydration on oral responding become more stimulus-specific: Oral responding to water is selectively enhanced after cellular dehydration, whereas extracellular dehydration selectively enhances responsiveness to both water and isotonic saline. This emerging selectivity in responding parallels previously described development of selectivity of intake in response to hydrational challenges (e.g., Hall & Bryan, 1981;Leshem & Epstein, 1988). For instance, in very young animals acute cellular dehydration equivalently increases intake of milk, water, and sucrose solutions in oral infusion tests (Bruno, 1981).…”

“…As pups mature, alterations in hydrational state have reduced effectiveness in enhancing intake of solutions other than water (e.g., Bruno, 1981;Leshem & Epstein, 1988). Likewise, although cellular and extracellular dehydration have marked effects on oral responsiveness to sucrose in 6-day-old pups, the changes in responding to oral infusions of sucrose become much less dramatic in older pups.…”

“…In young pups, dehydration enhances intake and responsiveness to sucrose; in older pups, dehydration either does not affect responding, or serves to suppress it. The suppressive effects of dehydration on responding to sucrose in older pups may reflect the emergence of the dehydration anorexia characteristic of adults and older pups (e.g., Bruno & Hall, 1982;Hsiao, 1970;Hsiao & Trankina, 1969;Leshem & Epstein, 1988).…”

“…It is not until 12 days of age that cellular dehydration produces greater enhancement of intake of oral infusions of water than oral infusions of milk (Bruno, 1981). Intake stimulated by angiotensin or renin administration is also relatively nonselective in young animals, with complete selectivity for enhanced water intake over milk intake emerging by 18 days of age (Leshem & Epstein, 1988). Although oral responsiveness to milk infusions were not investigated in the present study, the developmental changes in oral responding to sucrose and saline solutions following dehydration suggest that changes in oral responsivity to various tastants may mediate selective enhancement of intake following dehydration in older animals.…”