Study of the neural pathways concerned with involuntary movements induced by electrical stimulation of the mesencephalic ventromedial tegmentum in cats

A stimulating electrode was stereotactically implanted into the mesencephalic ventromedial tegmentum (VMT) in 15 adult cats. Immediately after stimulation of the VMT, an arrest reaction was observed, followed by contraversive turning and circling, and finally choreoathetoid movements in the contralateral forelimb and oro-bucco-lingual movements. An electrode was implanted in the dentate nucleus contralateral to the VMT in 3 cats. Stimulation of the dentate nucleus produced ipsilateral head tilting, followed by extension, elevation of forelimb and flexion of hindlimb. Electrolytic lesions were made in the dentate nucleus and thalamic VL-nucleus. Choreo-athetoid movements were diminished in dentatomized cats, and disappeared in VL-thalamotomized cats, but these lesions had no effects on bucco-lingual movements. To investigate the passing fibers in the VMT, horseradish peroxidase (Sigma type VI 0.060.08ul) was injected into the VMT in 12 cats. Labeled cells were found in the contralateral dentate nucleus, in the interposed nucleus, in the ipsilateral head of caudate nucleus and in the putamen. These results suggest that fibers passing through the VMT play an important role in the production of dyskinesias. Choreo-athetoid movements of limbs might be produced mainly by excitation of nigro-striatal and strio-pallido-thalamic pathways facilitated by the dentatethalamic pathway. These pathways are not involved in the production of bucco-lingual movements.