[Comparison of effects of systemic (intramuscular) and intrastriatal injections of D1-dopamine receptor blocker on motor behavior and postural adjustment in dogs]

Abstract

The study is based on the concept (Shapovalova, 2000) that activation and blockade of various types of muscarine and dopamine receptors located at various outputs of neostriatum should have different effects on motor behavior. The goal of the study was comparison of effects of systemic and intrastriatal injections of a selective blocker of D1 dopamine receptors on motor behavior. Experiments were carried out on 5 dogs on a model of instrumental defensive reflex (IDR) connected with keeping a certain flexor posture. Performance of the experiments, recording, storage, and analysis of data were accomplished with aid of original programs for PC. Systemic (intramuscular) administration of the blocker of D1 dopamine receptors SCH23390 at a dose of 0.025 mg/kg led to a sharp decrease of the IDR amplitude and in most cases--to the complete refusal of its performance. First of all, the phasic component of the instrumental response was inhibited, the diagonal pattern of the postural adjustment being preserved. Bilateral microinjections into the dog neostriatum of the same blocker of D1 receptors at a dose of 0.1 and 1.0 g did not change the percent of correct solution of the instrumental task, but at the same time produced a great number of changes in motorics: latent period of response increased statistically significantly, in some cases its amplitude rose, phasity decreased, intersignal raisings of limbs ceased completely. The obtained data allow the following conclusions to be made. 1. Difference of effects of systemic and intrastriatal injections of SCH23390 seems to be due to that at its systemic administration, D1 receptors of other structures, not only of neostriatum, can also be blocked. 2. Effect of nigrostriatal dopaminergic system on neostriatum via D1 receptors is complex - activation of motor activity (projectional spine neurons of the direct pathway) and a weak modulation of mental process (large spineless cholinergic interneurons). 3. Regulation of movement and postural adjustment is realized along different efferent neostriatum outputs.