Visualization of cortico-basal ganglia loop by means of transsynaptic transport of WGA-recombinant adeno virus and rabies virus

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Retrograde transneuronal labeling by means of transsynaptic transport of WGA-recombinant adeno virus and rabies virus was attempted to analyze the organization of functionally-related multi-synaptic pathways, for example, the cortico-basal ganglia loops that arise from various frontal motor and association areas. In this report, we have only described the data obtained from a series of experiments using rabies virus, because rabies virus was found to be much more sensitive than WGA-recombinant adeno virus for the present purpose. Injections of rabies virus (CVS-11; CDC) were made into the primary motor cortex (MI) to investigate the extent of its retrograde transport in the central motor system. A viral suspension was injected into the electrophysiologically identified forelimb region of the MI in rhesus monkeys. The monkeys underwent perfusion-fixation two to four days after the injection. Serial coronal sections were processed for immunohistochemical staining for rabies virus. Three … More days after viral injection, many second-order neurons were labeled, along with the first-order neurons in the thalamus and the cerebral cortex that project to the MI directly. In the basal ganglia, the labeled neurons were observed in the ventral aspect of the internal segment of the globus pallidus. Moreover, neuronal labeling occurred in the deep cerebellar nuclei, especially in the dorsal portions of the lateral and interpositus nuclei, and in several rostrally-situated motor-related areas of the frontal lobe. Around three and a half days after the injection, third-order neurons were seen in the ventral aspects of the putamen, the subthalamic nucleus, and the external segment of the globus pallidus, as well as in Purkinje cells of the cerebellar cortex and areas of the prefrontal cortex. In addition, our immunofluorescence analysis confirmed that cholinergic striatal interneurons and dopaminergic nigral neurons, probably fourth-order neurons in the basal ganglia, were labeled at the four-day postinjection period. Less