Involvement of the transmitter systems of the neostriatum in automation of motor skills in dogs.

Chronic experiments were performed on six dogs to address the influence of automation of a motor skill on the components of an operant defensive reflex, rearrangement of posture, and the characteristics of the projection of the center of mass on a tensometric platform by the forepaws; the effects of activation and blockade of muscarinic and dopamine receptors on the process of automation of the motor skill were also studied. Despite high criteria for execution of the operant reflex, the reproducibility of reflex performance, increases in the tonic component of the response, and the clear diagonal pattern of the postural rearrangement, a local (as opposed to diffuse) projection of the position of the center of mass on the tensometric platform by the forepaws was seen only after prolonged training leading to automation of the skill. The effect of automation of the operant response could be obtained immediately following bilateral microinjection of the muscarinic receptor agonist carbachol into the neostriatum. The same effect, but weaker, was obtained using bilateral microinjections of the dopamine D2 receptor blocker raclopride into the neostriatum. Conversely, bilateral microinjections of the selective muscarinic M1 receptor blocker pirenzepine into the neostriatum gave the opposite result, with increases in the phasic component of the response, impairment of the diagonal pattern of the postural rearrangement, and diffuseness of the projection of the center of mass on the tensometric platform by the forelimbs. It is concluded that the indirect efferent output of the neostriatum has an important role in the process of learning the motor operant reflex involving maintenance of a defined degree of flexion (where the main role is played by the tonic component of the movement) and during the process of automation of the motor skill.