| Research Abstract |
Basal ganglia disorders are characterized by the presence of abnormalities in the amount of movement and muscular tone. Gait disturbances are also major impediments for parkinsonian patients. It has been suggested that the basal ganglia control the amount of movement via thalamocortical. However, here, we provide evidence that control of muscle tone and locomotion is achieved via basal ganglia-brainstem systems. In the acute decerebrate cat, with the striatum, thalamus and cerebral cortex removed, trains of stimuli delivered to the mesencephalic locomotor region (MLR) produce controlled locomotion. In addition, trains of stimuli applied to the pedunculopontine nucleus (PPN) suppress postural muscle tone. Also, neuroanatomical studies have shown that MLR/PPN areas receive a GABAergic projection from substantia nigra pars reticulata (SNr), an output nucleus of the basal ganglia. Accordingly, we tested this system's function by activating it during MLR/PPN-controlled locomotion and postur
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al muscle tone. Repetitive stimuli delivered to SNr alone evoked no change in muscular activity. However, stimulation of the medial part of SNr suppressed MLR-evoked locomotion. At low strength, SNr stimulation reduced the number of MLR-activated step cycles and at higher stimulus strength, locomotion was abolished. Also, the onset of MLR-evoked locomotion was delayed as the strength of SNr stimulation was increased. These findings indicate that SNr contributes to both the initiation and the maintenance of MLR-induced locomotion. In addition, PPN-induced muscle tone suppression was attenuated at low-strength stimulation of the lateral portion of SNr, and abolished at higher stimulus strength. We further observed that the above SNr effects were blocked by injecting GABAA antagonists, into the MLR and PPN.These results all suggest that locomotion and postural muscle tone are subject to modulation by GABAergic nigrotegmental projections. The present work suggests that basal ganglia diseases may include dysfunction of nigrotegmental systems, with consequent disorders of gait and muscle tone. Less
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