EN
The motor unit (MU) contractile properties in medial gastrocnemius muscle of young Wistar Kyoto rats, the model of attention deficit hyperactivity disorder (ADHD), and normal Wistar rats were studied. Functional isolation of motor units was achieved by electrical stimulation of single axons from ventral roots of L4–L5 spinal nerves. The motor units parameters: the force of twitch and tetanus, the contraction and the half-relaxation times and the properties of action potentials were analyzed for 47 and 60 MUs in ADHD and normal rats, respectively. The three types of MUs (FF, FR and S) in both groups were found. The distribution of FF, FR and S MUs for normal rats was: 26.7, 55.0 and 18.3% whereas the distribution of FF, FR and S MUs for ADHD rats was: 27.6, 44.7 and 27.6%. There were no statistical differences in motor units force and twitch time parameters. However, the twitch-to-tetanus ratio was higher for MUs in ADHD animals. Moreover, differences between shapes of twitch recordings were found and a ratio of the contraction to the half-relaxation times was lower for MUs in ADHD animals. The mean number of turns of MU action potentials was lower in all types of MUs of ADHD rats.