SPONTANEOUSLY HYPERTENSIVE RATS (SHR) AS A PUTATIVE ANIMAL-MODEL OF CHILDHOOD HYPERKINESIA - SHR BEHAVIOR COMPARED TO 4 OTHER RAT STRAINS

Childhood hyperkinesis or attention-deficit hyperactivity disorder (ADHD) is a behavior disorder of which the main symptoms are attention problems and hyperactivity. The main objective of the present study was to investigate whether the spontaneously hypertensive rat (SHR) strain is a useful animal model of ADHD. Five different rat strains were tested: SHR, Wistar-Kyoto (WKY), Wistar, Sprague-Dawley (SPRD), and PVG (hooded) rats. The protocol consisted of three different test procedures: 1) A 7.5-min free-exploration open-field test (home cage accessible), where the SHR was less active than Wistar and SPRD but more active than WKY; SHR showed longer latencies to leave the home cage than both Wistar and SPRD rats, spending less time in the field, ambulating and rearing less than Wistar and SPRD but more than WKY. Within session, the SHR tended to be more active at the end of the session than at the start, while the opposite tended to be the case in the other groups. 2) A 7.5-min forced exploration open-field test (home cage not accessible), where the results showed that the SHR is less active than both the Wistar and Sprague-Dawley strains, but more active than PVG and WKY. 3) A two-component multiple schedule of reinforcement with a fixed interval 2 min signalled by houselight on and a 5-min extinction signalled by houselight off. Lever pressing by SHR was markedly different from that of the other four strains, which were quite similar. Except early in the interval, SHR pressed the lever more than any of the other groups. In addition, SHR pressed the lever more during the extinction component than did the other strains. This result may indicate that the SHR strain has a discrimination problem. Thus, the data show that SHR is not always the most active strain of rats in open fields when the sessions are short, but shows hyperactivity and problems of discrimination under the better controlled operant schedules of reinforcement. Therefore, the present study supports the previous suggestion that SHR may be a useful animal model of ADHD.