A loss of short-latency excitatory caudate unitary responses to motor cortex but not to motor thalamic nuclei stimulation in MPTP-treated cats.

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 5 mg/kg i.m. for 5 days) on the evoked activity of caudate neurones were studied extracellularly in ketamine-anaesthetized and myorelaxant-immobilized cats. Two days after the last MPTP injection the latency of caudate neurone responses to the motor cortex stimulation increased as compared to intact animals, due to a 10-fold decrease in the number of neurones with short-latency responses (from 1.8 up to 8.0 ms). At the same time, no essential changes were observed under the influence of MPTP in the distribution pattern of the latency of caudate neurone responses to the stimulation of the ventral anterior and ventral lateral nuclei of the thalamus. The suggestion that dopamine protects monosynaptic transmission of impulses from the cerebral cortex to neostriatum neurones is discussed.