Background: Although deficits of attentional set-shifting have been reported in individuals with attention deficit/\r\nhyperactivity disorder (ADHD), it is rarely examined in animal models.\r\nMethods: This study compared spontaneously hypertensive rats (SHRs; a genetic animal model of ADHD) and\r\nWistar-Kyoto (WKY) and Sprague-Dawley (SD) rats (normoactive control strains), on attentional set-shifting task\r\n(ASST) performance. Furthermore, the dose-effects of methylphenidate (MPH) on attentional set-shifting of SHR\r\nwere investigated. In experiment 1, ASST procedures were conducted in SHR, WKY and SD rats of 8 each at the\r\nage of 5 weeks. Mean latencies at the initial phase, error types and numbers, and trials to criteria at each stage\r\nwere recorded. In experiment 2, 24 SHR rats were randomly assigned to 3 groups of 8 eachââ?¬â?? MPH-L (lower dose),\r\nMPH-H (higher dose), and SHR-vehicle groups. From 3 weeks, they were administered 2.5 mg/kg or 5 mg/kg MPH\r\nor saline respectively for 14 consecutive days. All rats were tested in the ASST at the age of 5 weeks.\r\nResults: The SHRs generally exhibited poorer performance on ASST than the control WKY and SD rats. Significant\r\nstrain effects on mean latency [F (2, 21) = 639.636, p < 0.001] and trials to criterion [F (2, 21) = 114.118, p < 0.001]\r\nwere observed. The SHRs were found to have more perseverative and regressive errors than the control strains (p\r\n< 0.001). After MPH treatment, the two MPH treated groups exhibited significantly longer latency and fewer trials\r\nto reach criterion than the SHR-vehicle group and the MPH-L group exhibited fewer trials to reach criterion in\r\nmore stages compared with the MPH-H group. Significant main effects of treatment [F (2, 21) = 52.174, p < 0.001]\r\nand error subtype [F (2, 42) = 221.635, p < 0.01] were found.
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