Motor and cognitive functions of the neostriatum during bilateral blocking of its dopamine receptors

In experiments on 60 Sprague-Dawley rats, effects of systemic and intrastriatal injections of se-lective blocker of D1 receptors SCH23390 on elaboration of discriminational conditioned reflex of active avoidance (CRAA) were studied in T-maze and on behavior in test of the "open field". Systemic administration of this inhibitor at doses of 0.025 mg/kg produced a several fold decrease of percentage of correct realizations of the discriminational CRAA and of motor activity in the "open field" test. Bilateral microinjections of SCH23390 into the rat neostriatum at a dose of 0.004-1.0 mkg did not deteriorate learning of the discriminational CRAA as compared with intact control, although a marked inhibition of motor activity was observed in the open field, test. Analysis of the data has also shown a statistically significant decrease of percentage of errors in the starting maze compartment in experiments with intrastriatal injection of SCH23390 to rats. At the same time, the intrastriatal injection to rats of raclopride, a blocker of D2 dopamine receptors, at a dose of 0.004 mkg produced a sharp and prolonged deterioration of learning of the discriminational CRAA. The data obtained have allowed the following conclusions to be made: 1. Difference of effects of the systemic and intrastriatal SCH23390 injections seems to be due to that the behavioral changes observed at the systemic administration can be provided predominanantly by structures differing from neostriatal D1 receptors; 2. Effect of nigrostriatal dopaminergic system on the neostriatum through D1 receptors is complex: activation of motor activity (efferent spine cells of the direct pathway) and a poor modulation of the learning process (large aspine cholinergic interneurons); 3. The modulation of the learning process seems to occur through neostriatal D2 receptors (large aspine cholinergic interneurons).     

Effect of microinjections of a selective blocker of M1-muscarinic receptors pirenzepine into the neostriatum on the rat motor activity

In simulated discrimination conditioned reflex of active avoidance (CRAA) in T-maze, the effect of bilateral microinjections of the muscarinic receptor M1 selective blocker pirenzepine on the CRAA formation and behaviour in the "open filed" test, was studied in rats. A sharp worsening of the CRAA learning and a significant increase in the motor activity were shown to occur in rats following the microinjections as compared with control rats. The change in the motor responses seems to account for the worsening of the CRAA learning. Another reason of the phenomenon could involve a disorder in perception of conditioned signals and their poor differentiation. The data obtained and the literature data suggest a complex character of changes induced by the blockade of the M1 muscarinic receptors of the neostriatum.     

Instrumental behavior in the activation or blockade of the neostriatum muscarinic receptors

In four dogs, microinjections of carbacholine enhanced the tonic component and inhibited the physical component of the instrumental defence reflex, put in order the posture, and increased its components' amplitude. Microinjections of raclopride yielded a similar though a less obvious result. Differentiation stimuli provided the greatest effect of both substances. A sharp improvement occurred in differentiation of sound signals. Microinjections of pyrenzepine yielded an opposite result. The data obtained are explained proceeding from the idea of a presence of the neostriatum's two efferent outputs exerting opposite effects on their targets, and the role of muscarine and dopamine receptors in their triggering and blockade.