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Understanding the role of the dopamine system in learning and memory processes is very important for uncovering central mechanisms underlying complex behavioral responses that can be impaired in patients with neuropsychiatric disorders caused by dopamine system dysfunction. One of the most useful animal models for dopaminergic dysregulation is the strain of dopamine transporter knockout (DAT-KO) rats that have no dopamine re-uptake and thus elevated extracellular dopamine levels. It is known that dopamine is involved in various cognitive processes such as learning, memory and attention. This investigation was focused on the ability of DAT-KO rats to learn and perform a behavioral task in the 8-arm radial maze test. It was found that DAT-KO rats are able to learn the behavioral task, but the level of task performance did not reach that of WT group. The behavioral tactics used by animals during training significantly differ in mutants. The behavioral tactics used by DAT-KO rats involved perseverations and resulted in worse task fulfillment in comparison to wild-type controls. The data obtained indicate that deficient dopamine reuptake results in an impairment of working memory and perseverative behavioral tactics in DAT-KO rats.

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Study of peculiarities of formation of preference in use of one of forelegs at learning of the manipulatory food-procuring skill has been carried out at different stages of early ontogenesis of white rats. It was established that as early as at the 3-week age the rat pups were already able to learn getting food from a narrow test-tube; however, no expressed preference in using one of the extremities was revealed. After repeated testing of adult rats at the age of 4 months the number of ambidexters was significantly higher than in the control animal group. At learning of the 30-day old rat pups of this manipulatory skill, in the majority of the rat pups, no significant lateralization also was found in using the foreleg. At repeated testing of adult rats the amount of ambidexters did not differ from that in the control group of animals. The obtained results indicate the existence of critical periods in formation of lateral preference in performance of the manipulatory food-procuring skill. There also was shown effect of learning in early ontogenesis on the capability for lateralization of this skill in the adult state in rats.

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A very dilute solution of Nux Vomica 200 plant alkaloid was applied onto the tongue of Wistar rats. The level of rats' anxiety was estimated by their behavior in elevated plus-maze. The dry application led to substantial changes in rats' behavior. In "passive" rats previously defined by the forced swimming tests changes in behavior were most prominent. The possible influence of the drug under study on the adaptive abilities of this group of animals is discussed.

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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.

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The effects of microinjections of D1 selective dopaminergic substances into the medial frontal cortex (MFC) on information storage and proactive interference during delayed (the delay in 3 s) and non-delayed choice in Y-maze were studied. Bilateral microinjection of D1 receptor antagonist SCH 23390 (1 nM, 1 microliter) impaired both delayed and non-delayed choice. In contrast, microinjections of D1 receptor agonist SKF 38393 (1 nM) into the MFC significantly improved the delayed performance and did not influence the non-delayed choice. The effects of proactive interference caused by SCH 23390 and SKF 38393 injections were more pronounced in delayed choice condition than in the non-delayed task. Spatial bias in animal behavior was revealed after the SCH 23390 injections: during erroneous choices rats more frequently turned in the same direction as preferred in a rotation test. The results suggest that impairment of delayed performance in Y-maze observed under the blockade of D1-mediated neurotransmission in the MFC occurs due to enhancement of the processes of proactive interference and disinhibition of the spatial set.

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The study examined the effects of modulation of dopamine D2 receptors-mediated neurotransmission in the rat's prefrontal cortex (PFC) on storage and executive components of working memory. Rats were trained on delayed (delay interval, 3 s) and non-delayed choice in a U-maze. The prominence of proactive interference was evaluated by sorting errors in a current trial on the basis of animal reactions in a preceding trial. The erroneous runs to the same arm of the maze as in the previous trial were identified as the repetitions (RE) and the erroneous runs to the other arm in comparison with the previous trial were classified as alternations (AE). The bilateral microinfusion of D2 agonists PPHT (0.004 microg, 0.04 microg, 0.4 microg/1 microl) into medial wall of the PFC produced a dose-dependent increase in the error rate of the delayed-response task and did not influence non-delayed choice. In delay condition PPHT enhanced the perseverative tendencies (the rate of RE was significantly higher than the rate of AE), in non-delayed choice the erroneous performance was mainly represented by AE. In contrast, the infusion of D2-receptor antagonist sulpiride (0.03 microg, 0.3 microg, 3 microg/1 microl) increased the accuracy of delayed choice and changed the mode of intertrial dependence-rats made significantly more AE than RE. The results are discussed in terms of the involvement of D2 receptor dependent transmission of the PFC in different cognitive processes related to the delayed performance in U-maze (within-trial short-term storage of information versus dynamic control of between-trials working memory processing).

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The influence of the preceding conditioned reaction on the current conditioned performance was studied. Rats were trained to perform delayed and non-delayed spatial tasks in Y-maze. Two types of errors were analyzed: 1) the rats ran to the same maze arm as in the previous trial (errors of repetition), 2) the animals ran to the other arm (errors of alternation). It was shown that the alternation errors were more frequent under conditions of short intertrial interval and non-delayed choice. The repetition errors occurred more frequently under conditions of long intertrial interval and delayed choice. The obtained evidence supports the idea that not only cue presentation and delay periods are important for successful performance but the whole structure of the task influences the complex organization of the behavioural acts.

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The activity of neurons of the medial wall of the frontal cortex (MWFC) of the brain of rats trained to a delayed spatial choice task was investigated. Significant reorganizations of the activity of the neurons were found when the motivational state of the animal was changed. Direct connections were identified between hypothalamic nuclei and the MWFC using the retrograde axonal horseradish peroxidase transport method. The role of hypothalamocortical interactions in providing the motivational-emotional components of behavior is discussed.

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Unit activity of the medial wall of the frontal cortex was studied during spatial delayed performance in rats. Significant modifications of the neuronal activity were observed after the change of motivation. Direct neuronal projections from hypothalamic nuclei to the medial wall of the frontal cortex were revealed by horseradish peroxidase technique. The role of hypothalamo-cortical interaction in organization of motivational and emotional components of behaviour is discussed.

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The activity of neurons of the medial wall of the frontal cortex of the brain of rabbits was investigated during their performance of a task of delayed spatial choice. The recording of neuronal activity was carried out in two groups of animals which were at different stages of training. Different types of spatially selective neurons were found. The possible association of the character of the neuronal reorganizations with the level of learning of the animal is discussed.

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Unit activity of the medial wall of the rat prefrontal cortex was studied during delayed response of spatial choice. Recording was performed in two groups of animals at different levels of learning. Several types of spatio-selective neurones were revealed. Probable relationships of unit activity changes and level of learning are discussed.

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Unit activity of the medial wall of the rat prefrontal cortex was studied during delayed response in the U-shaped maze. Prefrontal units were shown to be polysensory. Rhythmical stimulation induced habituation of unit responses. Spatio-selective neurones were found which means that medial part of the prefrontal area is involved in short-term memory. The role of the area is discussed in relation to the goal-directed behaviour.

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The unit activity of medulla oblongata extracellularly recorded during stimulation of the taste receptors and skin chemoreceptors with solutions of the hydrochloric and citric acids, sodium chloride and potassium chloride, in the majority of neurons responded at least to the solutions of one acid and one salt. The number of units which responded to all the solutions was twice as high on stimulation of taste receptors than skin chemoreceptors. The chemical stimuli graduation analysis is more suitable in the case of taste receptor stimulation. The peculiarities of the primary center unit activity response to the stimulation of the receptive fields in question may be connected with different role of taste and skin chemoreceptors in adaptive behaviour.

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