Exclusively drinking sucrose or saline early in life alters adult drinking behavior by laboratory rats.

Proper fluid balance is critical for life. Learning plays an important role in shaping the appetitive behaviors required for drinking. Children often forego drinking plain water and instead consume beverages such as milk or juice. What effect this may have on adult thirst responses remains an open question. To model aspects of the human condition, we bred Sprague-Dawley rats and prevented the pups from obtaining fluid other than from nursing. Pups were weaned onto either tap water, 5% sucrose, or 0.45% saline, and given access to only that fluid for at least 7 weeks. We then measured intake of water or sucrose/saline in one-bottle tests after mild hypertonic saline (HS) injection, or overnight fluid deprivation, and in two-bottle tests after HS injection while rats were maintained on their respective fluids, and after all subjects had only water to drink for a week. We found that sucrose- and saline-maintained rats drank less water than did controls after the HS challenge. After overnight fluid deprivation, rats maintained on saline drank less water and more saline, but there was no difference in intake between water-maintained and sucrose-maintained rats. Differences in licking patterns, including more licks/burst for sucrose by sucrose-maintained rats were detected, even in cases when total intake was not different. These data provide evidence that adult rat water intake can be reduced by exclusively drinking sucrose or saline early in life.