Is the Lewis (LEW) Rat an appropriate control for the Spontaneously Hypertensive Rat (SHR) on a delay discounting task?

The Spontaneously Hypertensive rat (SHR), the most widely accepted rodent-model of Attention Deficit/Hyperactivity disorder (ADHD), is compared with its normotensive control the Wistar Kyoto (WKY) rat looking for between strains differences in impulsive choice. But the WKY is not a proper control for the SHR when the procedure requires locomotion to choose. The SHR has deficiencies in dopamine activity in nucleus accumbens causing lower tolerance to delayed outcomes than the WKY. Locomotion and anomalies in dopamine in the Lewis (LEW) rat are like those in the SHR, suggesting that the LEW is a good control for the SHR. This possibility was analyzed with SHRs and LEWs responding to concurrent-chains procedures. Choice was measured in the initial link where two random interval schedules arranged entries to two terminal links, one delivering 1-food pellet immediately and the other delaying 4-food pellets 0.1, 5, 10, 20, 40, or 80 s. Impulsive choice increased with increasing training, but the SHRs shown faster changes in preference making more impulsive choices than the LEWs. The hyperbolic-decay model and the generalized matching law fitted the data well. Positive correlations between discounting rate and sensitivity of choice to the immediacy of reinforcement suggest compatibility between models of choice