DELAY DISCOUNTING AND POLYDIPSIA IN SPONTANEOUSLY HYPERTENSIVE (SHR) AND LEWIS (LEW) RATS

This study compared the performance of the Spontaneously Hypertensive rat (SHR) on a delay discounting task with the performance of the Lewis rat (LEW) to suggest that both strains of rats are potential models of Attention Deficit/Hyperactivity Disorder (ADHD). It measured choice in the initial link of a concurrentchains procedure with presses on two levers arranging entries to two terminal links, one delivering 1-food pellet after a 0.1-s delay and the other 4-food pellets with delays of 0.1, 5, 10, 20, 40 or 80 seconds presented in random order during the session. A bottle with tap water could be available for the rats to drink during the session (B), or it was not available (A) according to an ABABA reversal design. The SHR and LEW rats made impulsive choices producing discounting functions showing discounting rates increasing with increasing training sessions. Early in training the SHR rats produced discounting rates greater than the LEW rats, but at the end of training both strains of rats produced comparable discounting rates. All rats developed polydipsia in condition B, but the SHR rats consumed more water and emitted more licks than the LEW rats. Polydipsia was not linked to discounting rate, nor polydipsia caused the rats’ impulsive choices to decrease.