Effect of aging on fluid ingestion in mice.

The amount of fluid consumed by C57BL/6Nnia male mice 3, 12, and 25 months of age under various paradigms was studied. The old mice consumed less water during the dark cycle but not during the light cycle (12 h lights off; 12 h lights on). When thirst was induced by providing dry food pellets or after overnight fluid deprivation, old mice consumed significantly less water than younger mice over a one-hour period. When thirst was induced by administration of hypertonic saline, there were no age-related effects. Naloxone 7.5 mg/kg IP significantly suppressed drinking in 3- and 12-month-old mice, while 25-month-old mice did not show suppression. Dehydration-induced thirst is impaired in old mice, as it is in older humans. This may be related to the alteration in opioid mechanisms modulating thirst.