Increasing the activity of the neostriatum cholinergic system alters an established type of motor behavior in animals

Chronic experiments on four dogs were performed to study the effects of bilateral microinjection of the choline receptor agonist carbacholine and the blocking agent scopolamine into the dorsolateral part of the head of the caudate nucleus on the performance of an operant defensive reflex involving maintenance of a specified amount of flexion and on the differentiation of meaningful signals. Bilateral microinjection of carbacholine (0.1-0.4 micrograms in 1.5 microliters of solvent) reduced the phasic component and amplified the tonic component of the operant responses, inhibited intersignal leg lifts, normalized posture, and calmed the animals, and also led to a sharp improvement in the differentiation of meaningful signals. These changes were expressed as increases of three-fold or more in the latent period of movement initiation when the differentiation signal was used, as compared with the baseline latent period before the injections. Microinjection of the choline receptor blocker scopolamine into the striatum had the opposite effects. Unilateral microinjection of these substances produced changes mainly only on the day of dosage and had no effect on subsequent behavior, while bilateral microinjection altered the established motor behavior for a longer period of time. This affected both the motor and the sensory components of the operant response.