[Muscarinic receptors of the neostriatum -- important targets of regulation of instrumental movement and posture].

Chronic experiments with 10 dogs were conducted to study effects of bilateral microinjections of the nonselective agonist of the muscarinic receptors carbachol, nonselective blocker of the muscarinic receptors scopolamine and selective blocker M1 of the muscarinic receptors pyrensepine on the instrumental defensive reflex in the neostriatum to sustain a given flexion amplitude and posture adjustment. Microinjections of carbachol were found to increase tone and stem the phase of the reflex, make posture adjustment more orderly and amplitudinous. Repeated microinjections gave the instrumental movement a ramp-like form. Chronic carbachol microinjections (over several years) resulted in akinesis and rigidity in dogs. However, these led to impairment of the diagonal pattern of posture adjustment as in pathologic so in normal dogs. These developments were partially meliorated by dopamine, scopolamine and pyrensepine which sharply increased the phase component of the instrumental movement. These findings are interpreted in the light of the concept of two neostriatum efferent outputs with opposite effects on respective targets and the muscarinic and dopamine receptors as their triggers and blockers. Results of the experiment bring to the conclusion that activation or blockage of the muscarinic receptors in the neostriatum can modify an existing motor behavior and compensate motor pathology in dogs.