Cholinergic Mechanism of Brain Involved in Compulsive Circling

Abstract

Compulsive circling, directed either to the left or to the right, can be produced in rabbits by the injection of 0.05, 0.10 or 0.15 mg/kg of DFP into the right common carotid artery. A study of the effects of these doses of DFP on the ChE activity in the frontal cortex, caudate nucleus, superior and inferior corpora quadrigemini, and thalamus of circling animals has been presented. An asymmetric ChE pattern in the cortex and caudate nucleus was always associated with the involuntary circling behavior. However, no asymmetry in ChE activity was noted between corresponding posterior right and left brain areas (medulla, pons, cerebellum). In these experiments the vestibular nuclei were not involved in the production of forced circling. The injection of either ACh (10–100 µg/kg) or Mecholyl (25–50 µg/kg) through a ‘T’ shaped cannula inserted into the right common carotid artery produced forced turning movements of short duration in a majority of the cases. Although a few animals turned to the left, most rabbits circled to the right. These experiments present additional evidence for the intermediary role of ACh in the production of compulsive circling after the injection of DFP. The evidence suggests a cholinergic mechanism in the cerebral cortex and caudate nucleus for the production of forced circling in rabbits. An hypothesis based on the ChE activity in these structures has been presented which can explain why these animals exhibit forced turning movements under the experimental conditions.