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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 effects of local microinjections of D1-selective dopaminergic agents into the medial wall of the frontal cortex of rats on short-term memory processes were studied, along with the effects of proactive interference in immediate and delayed spatial choice tasks in a Y maze. Microinjections of the D1 receptor antagonist SCH23390 (1 nmol) disturbed performance of both immediate and delayed choice tasks. while administration of the D1 receptor agonist SKF38393 (1 nmol) had no effect on immediate choice and improved delayed performance. The effects of proactive interference, induced by microinjections of SCH23390 and SKF38393 into the frontal cortex, were significantly more marked in delayed choice than in the non-delayed task. Administration of SCH23390 increased the number of erroneous excursions made by the animals, the directions of these excursions coinciding with the preferred direction of rotation of the animals in a rotation test. The results obtained here lead to the conclusion that blockade of dopaminergic transmission in the mediofrontal cortex of rats worsens the performance of spatial choice in a Y maze by strengthening proactive interference processes and disinhibiting the mechanisms which intemally prepare the animals to respond to a defined spatial direction with behavioral acts.