Attention deficit hyperactivity disorder (ADHD) is believed to be connected with a high level of hyperactivity caused by alterations of the control of dopaminergic transmission in the brain. The strain of hyperdopaminergic dopamine transporter knockout (DAT-KO) rats represents an optimal model for investigating ADHD-related pathological mechanisms. The goal of this work was to study the influence of the overactivated dopamine system in the brain on a motor cognitive task fulfillment. The DAT-KO rats were trained to learn an object recognition task and store it in long-term memory. We found that DAT-KO rats can learn to move an object and retrieve food from the rewarded familiar objects and not to move the non-rewarded novel objects. However, we observed that the time of task performance and the distances traveled were significantly increased in DAT-KO rats in comparison with wild-type controls. Both groups of rats explored the novel objects longer than the familiar cubes. However, unlike controls, DAT-KO rats explored novel objects significantly longer and with fewer errors, since they preferred not to move the non-rewarded novel objects. After a 3 months’ interval that followed the training period, they were able to retain the learned skills in memory and to efficiently retrieve them. The data obtained indicate that DAT-KO rats have a deficiency in learning the cognitive task, but their hyperactivity does not prevent the ability to learn a non-spatial cognitive task under the presentation of novel stimuli. The longer exploration of novel objects during training may ensure persistent learning of the task paradigm. These findings may serve as a base for developing new ADHD learning paradigms.
The problem of motor lateralization in ontogenesis is important for understanding adaptation development. In our experiment adolescent (P28-P30) and adult (P120) rats were trained in an eight-arm radial maze and their motor behaviour compared during training. During learning, the adult rats typically started by moving either left or right direction in the central arena in choosing the way in the maze. The adult rats also developed behavioural tactics to enter maze arms at 45° or 90° relative to the previously visited arm. The adolescent rats showed no directional preference and no clear behavioural tactics when entering maze arms. Based on our findings, we propose that motor lateralization increases the efficacy of food search and leads to the elaboration of behavioural tactics. Data obtained may reflect the fact that motor behaviour specialization develops gradually during ontogenesis and is helpful for adaptation to the environment.
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