Three water restriction schedules used in rodent behavioral tasks transiently impair growth and differentially evoke a stress hormone response without causing dehydration.

Water restriction is commonly used to motivate rodents to perform behavioral tasks; however, its effects on hydration and stress hormone levels are unknown. Here, we report daily body weight and bi-weekly packed red blood cell volume and corticosterone in adult male rats across 80 days for three commonly used water restriction schedules. We also assessed renal adaptation to water restriction using post-mortem histological evaluation of renal medulla. A control group received ad libitum water. After one week of water restriction, rats on all restriction schedules resumed similar levels of growth relative to the control group. Normal hydration was observed, and water restriction did not drive renal adaptation. An intermittent restriction schedule was associated with an increase in corticosterone relative to the control group. However, intermittent restriction evokes a stress response which could affect behavioral and neurobiological results. Our results also suggest that stable motivation in behavioral tasks may only be achieved after one week of restriction.Significance statementNeuroscience research has seen the growing use of water restriction in studies using head-fixed rodents. Despite this growing use, the effects of various water restriction schedules on hydration and stress hormone levels are unknown. Here, we assess hematocrit and blood corticosterone over 80 days and compare three commonly used restriction schedules. Our results show that one type of restriction schedule evokes a stress response, which may have unanticipated neurobiological and behavioral consequences.