| Research Abstract |
In subprimates, the pedunculopontine nucleus (PPN) has the direct projections to the spinal cord, and these descending projections have been investigated in detail. However, the relationship of the descending projections of basal ganglia with the reticulospinal projection systems still remains unresolved in the monkey. We attempted to clarify the distributions of the ponto-mesencephalic neurons projecting to the lower brainstem and the spinal cord, and their relation to the basal ganglia in monkeys. The following conclusions were obtained :
The pallidotegmental projections arise from the caudal ventrolateral part of the medial pallidal segment (GPi), and terminate mainly in the dorsolateral part of the pedunculopontine nucleus (PPN) located lateral to the decussation of the superior cerebellar peduncle. On the other hand, mesencephalic tegmental neurons projecting to the spinal cord and/or nucleus reticularis gigantocellularis (Gi) were located outside the usual boundaries of PPN. PPN neurons projecting to the spinal cord and to the Gi might be quite few, if any, in the monkey. The PPN receives the basal ganglia transmitting information from the ventrolateral part of caudal GPi, and convey it to the spinal cord and Gi via interneurons connecting to the lateral periaquetal gray-and adjoining mesencephalic tegmentum including the nucleus cuneiformis, and the rostral and caudal pontine nuclei. The interneuronal connections remain to be established. The PPN also receives autonomic afferents from the medial prefrontal area, and acts as an important interface between the basal ganglia and the brainstem motor system and is implicated in the control of posture and locomotion. The Gi receives cortical afferents directly from the ventral and dorsal premotor areas, and polysynaptically from the primary motor cortex through the basal ganglia-brainstem centers, and plays an important role in locomotion.
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