Reciprocal and additive effects of hyperoncotic and hypertonic treatments on feeding and drinking in rats

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.

Section: Resultssupporting

confidence: 92%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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

Leshem

Epstein

1988

“…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).…”

Section: M Naclmentioning

confidence: 99%

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

Swithers

1995

Hydrational state has been demonstrated to influence intake of various solutions in young rat pups. For instance, both cellular and extracellular dehydration produce an enhancement of intake in pups tested at 6 days of age. However, the behavioral mechanisms that result in increased intake following manipulations of hydrational state have been less extensively studied. The impact of hydrational state on behavioral responsiveness in young rat pups was examined by assessing the pattern of responding to a series of repeated oral infusions of diet. Pups were tested at 6, 12, or 18 days of age following either acute cellular dehydration produced by injection of 1 M NaCl or acute extracellular dehydration produced by injection of 10% polyethylene glycol (PEG). Oral responsiveness to a series of 30 brief infusions of one of four taste solutions (water, 10% sucrose, 0.135 M NaCl, or 1 M NaCl) was measured. Each infusion lasted 3 s and there was 1 min between infusions. The pattern of oral responding to solutions was affected by the developmental age of the pup, the hydrational state of the pup, and the solution offered, with the largest effects of dehydration observed in the youngest animals. In all conditions except one, pups habituated to repeated infusions. The exception was the failure of extracellularly dehydrated 6-day-old pups to display habituation to oral infusions of sucrose. These results suggest that, although intake is enhanced by both cellular and extracellular dehydration in very young pups, the behavioral changes responsible for the enhancement of intake after cellular dehydration are different from the behavioral changes resulting from extracellular dehydration. This dissociation of behavioral effects of dehydration in young pups demonstrates that intake measures alone may obscure subtle differences in behavior and argues for the utility of dissection of behavioral components in understanding the neural and physiological control of behavior.

Olfactory contributions to dehydration‐induced anorexia in weanling rats

Bruno

Hall

1982

By 20 days of age, dehydration produces a clear anorexia, even though weanling rats have had only limited feeding and drinking experience. Their lack of ingestive experience makes weanlings good subjects for studying the physiological mechanisms subserving anorexic phenomena because learned contributions are unlikely to add significant complications. Twenty-day-old rats dehydrated by hypertonic saline injection were anorexic when offered milk or solid food (rat chow), but not when offered sucrose solutions (Experiment I). However, when the scent of almond was associated with sucrose solutions, or with water, intake of these solutions was depressed by dehydration (Experiment II). Thus for dehydrated rats, olfactory stimulation may help produce dehydration-induced anorexia. Making rats anosmic by intransal lavage with ZnSO4 (Experiment III) eliminated the anorexia to almond-scented water and partially eliminated that to milk. For these fluids, an odor cue seems a requirement for the occurrence of dehydration-anorexia. In Experiment IV, we found that dehydration-anorexia did not occur when milk was infused directly into pups' mouths. This finding suggests that the inhibitory process mediating dehydration-anorexia influences the approach to food and not the actual consumatory response that occurs once food is in the mouth. The inhibition of feeding produced by dehydration, therefore, may depend largely on olfactory cues, and seems to operate at a distance, as rats locate and approach food.