Further evidence for the role of the caudate nucleus in programming motor and nonmotor behavior in Java monkeys

This study describes the short-term effects of intracaudate microinjections of carbachol in temporarily isolated and restrained Java monkeys. The monkeys were found to display a series of motor disturbances including blepharoptosis, facial twitches, tongue protrusions, ear flattening, torticollis, and compulsive alternations of rapid flexions and extensions of the extremities. In general, carbachol was found to produce consistent effects as far as it concerns its ability to elicit motor disturbances. Three of the five tested monkeys had previously received another series of carbachol injections when they were freely moving and living in a stabilized social group. Accordingly, the present study enabled us to compare the effectiveness of threshold doses of carbachol in the same monkey in two distinct situations. We concluded first, that motor disturbances and disturbances in social communication were closely coupled in relation to the involvement of a particular cholinoceptive substrate within the caudate nucleus of Java monkeys. Second, the motor disturbances under study appeared to require a larger degree of dysfunctioning of this substrate than did subtle disturbances in the social communication of these monkeys. And, finally, stress inherent to restraint increased the susceptibility of the cholinoceptive substrate within the caudate nucleus. The clinical impact of our findings is discussed in view of differences between the premorbid and manifest phases of Parkinson's disease.