A basic study of the motor disturbance in basal ganglia diseases

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We planned to study the synaptic organization of the rat parafascicular nucleus (Pf) of the thalamus, which projects to the striatum, in relation to parafascicular afferents. After injections of biotinylated dextran amine (BDA) into the superior colliculus (SC) or the pedunculopontine tegmental nucleus (PPN), both of which are main afferent sources of the Pf, numerous BDA-labeled axons and axon terminals appeared in the lateral part of the Pf. Electron microscopically all of the labeled axon terminals contained round synaptic vesicles and made asymmetric synapses. Comparing SC and PPN afferent terminals, the former seemed larger than the latter, and SC terminals tended to be located at more proximal portion of dendrites than PPN terminals. When wheatgerm agglutinin conjugated to horseradish peroxidase (WGA-HRP) and BDA were injected into the striatum and SC, respectively, BDA-labeled terminals were observed to synapse with WGA-HRP labeled Pf neurons. Thus, the serial colliculo-parafasciculo-striatal projection was proved. When WGA-HKP and BDA were injected into the SC and PPN, respectively, axon terminals from both nuclei observed to synapse with a single dendrite of Pf neurons. This fact means that SC and PPN afferents converged onto a single Pf neuron. It is conceirvable, therefore, both ocular and orientation movements of the SC function, and locomotion of the PPN function are integrated in the Pf. Then this kind of information might be sent to the striatum, and conveyed to the motor cortex via the basal ganglia circuitry. Now we could explain a part of the Pf function.