[Neuroanatomical study of experimental tremor produced by VMT lesion in monkeys--a horseradish peroxidase study]

Destruction of the ventromedial tegmentum (VMT) of the midbrain in monkeys is known to produce tremors similar to those seen in Parkinson's disease. To elucidate such tremorgenic mechanisms, 50% horseradish peroxidase (HRP) was injected into the VMT target region in three monkeys (macaca fuscata fuscata) and eleven adult cats. The volume injected varied between 0.05 and 0.1 microliter. The results suggest that afferent fibers to the thalamus, which passed through the VMT region, contains tractus cerebellothalamicus and nigrothalamic fibers. A large number of labelled cells were found in the ipsilateral nucleus dorsalis raphae, indicating that serotonergic neurons are related to the experimental tremors. Many labelled terminals were observed in the ipsilateral nucleus subthalamicus in the monkey, but in cats no terminals were found. This suggests that VMT region in the monkeys contains nigrosubthalamic fibers. The experimental tremors produced by destruction of the VMT region in the monkeys appears to be due to combined destruction of the tractus cerebellothalamicus, nigrothalamic fibers, tractus nigrostriatus, ascending serotonergic neurons from the nucleus dorsalis raphae and nigrosubthalamic fibers.