Caudate nucleus and programming behaviour in cats: role of dopamine in switching motor patterns

Cats were trained to walk on a specially designed treadmill: the cats were able to collect food pellets by switching motor patterns with or without the help of exteroceptive stimuli inherent to the treadmill. To study the involvement of the caudate nucleus in switching motor patterns cats received intracaudate bilateral injections of haloperidol. In addition, in a final series of experiments, EMG recordings of two antagonistic muscles, together with recordings of characteristic changes in the length of one muscle, were made before and after the haloperidol treatment. Haloperidol treatment resulted in a decreased number of motor patterns which were not directed by exteroceptive stimuli (non-exteroceptively directed motor patterns). This haloperidol-induced effect was dose-dependently counteracted by the additional intracaudate injections of apomorphine which per se remained ineffective. Haloperidol neither altered the number of food collecting attempts nor reduced the number of exteroceptively directed motor patterns. Furthermore, haloperidol did not affect the capacity to switch to proprioceptively directed motor patterns. Finally, haloperidol did not produce abnormalities in EMG and length signals recorded from hindlimb muscles. It is concluded that haloperidol selectively reduced the animal's capacity to 'programme non-stimulus directed motor behaviour'. The data are discussed in view of their significance for therapy of patients with basal ganglia disorders, such as patients suffering from Parkinson's disease.