The behavior of spontaneously hypertensive and Wistar Kyoto rats under a paced fixed consecutive number schedule of reinforcement

Spontaneously hypertensive (SHR) and Wistar Kyoto rats (WKY) were trained under paced FCN schedules of reinforcement to complete a minimum number of consecutive responses on one lever, before responding on a second. The levers were retracted from the test chamber for a short period after each response to control the speed at which the rats could complete the sequence (paced FCN). Changes in the average chain length may reflect the influence of impulsivity on the execution of behavioral patterns. Although they quickly learned to press the levels, SHR rats performed poorly compared to the WKY rats when the chain length requirement was increased to FCN 6 and FCN 8. Eventually stable performance was obtained under paced FCN 6, although the SHR rats continued to have a consistently lower average chain length. Both strains of rats were treated with imipramine (10 mg/kg), chlordiazepoxide (3 and 10 mg/kg), d-amphetamine (0.4 and 0.8 mg/kg), haloperidol (0.05 and 0.1 mg/kg), 8-OH-DPAT (0.1 mg/kg), WAY-100635 (0.1 mg/kg), and DOI (0.3 and 1.0 mg/kg). The SHR rats were less sensitive to the effects of d-amphetamine, chlordiazepoxide, and DOI and slightly more sensitive to the effects of haloperidol. All of these drugs reduced the average chain length. There was no difference in the response of the two strains to imipramine and 8-OH-DPAT, both of which increased the average chain length. These results support the suggestion that SHR rats may more impulsive than WKY rats. The data with d-amphetamine and haloperidol support biochemical findings that these rats have a deficit in dopaminergic function, and the strain differences in response to chlordiazepoxide and DOI suggest that that there may be differences in GABAergic and 5-HT2-mediated neurotransmission relevant to regulating impulse control in the rat. (C) 1999 Elsevier Science Inc.