INCREASED SUBTHALAMIC NEURONAL-ACTIVITY AFTER NIGRAL DOPAMINERGIC LESION INDEPENDENT OF DISINHIBITION VIA THE GLOBUS-PALLIDUS

Electrophysiological records of unit activity were used to compare the effects of excitotoxic pallidal lesions and 6-hydroxydopamine-induced damage to the midbrain dopaminergic neurons on the discharge rates an d patterns of the subthalamic neurons. Removal of the pallidal input i nduced a slight, but statistically significant, increase (19.5%) in th e discharge rate and no change in the firing pattern when compared to control animals. The rats with a dopaminergic lesion showed greater in crease (105.7%) while the firing pattern activity of the subthalamic n eurons became more irregular, with bursts. These results indicate that the increased activity of the subthalamic neurons following a midbrai n dopaminergic lesion cannot be due solely to inhibition-disinhibition involving the striato-pallido-subthalamic pathway and induced by the striatal dopaminergic depletion.