Experimental tremor produced by ventromedial tegmental lesion in monkeys. Neuroanatomical study

Destruction of the ventromedial tegmentum (VMT) of the midbrain in the monkey has been known to produce tremor similar to that seen in Parkinson's disease. A neuroanatomical study by a silver impregnation method was conducted on 5 monkeys, demonstrating the characteristic flexed posture with hypokinesia of the contralateral upper limb (reliable premonitory sign of tremor) following destruction of VMT with a histologically proven lesion site. The results are summarized as follows: (1) the tractus nigrostriatus, (2) tractus tegmentalis centralis, (3) ascending fiber bundles going to the thalamus (particularly VL.X and VPLo) and (4) descending fibers leading to the bilateral substantia nigra constitute the bulk, if not all, of those neural tracts which pass through the VMT. This, along with the proven existence of fibers projecting to the thalamic nuclei, is thought to account for the rhythmic burst discharges recorded from the VL or Vim nucleus in the monkey and in Parkinson's disease patients. The present experimental study also seems to provide an additional anatomical basis for the concept that the tractus tectonigralis is involved in the mechanism of development of kinésie paradoxale.