Substantia nigra and somatosensory evoked responses in the caudate nucleus.

The nigro-caudate relationships were studied in fifteen adult anesthetized cats, paralyzed with Flaxedil. Single shocks applied to substantia nigra (SN) evoked biphasic field potentials in the ipsilateral caudate nucleus. Similar positive-negative waves were recorded in the caudate nucleus by sciatic stimulation, although with longer latencies. A triphasic field potential was also observed after cerebral peduncle stimulation. Conditioning stimuli applied to the SN at varying time intervals prior to sciatic stimulation did not modify the test response. In contrast, conditioning stimulation of the cerebral peduncle produced a marked inhibition between 25 and 100 msec. Recovery was complete after 200 msec. The present observations indicate that nigral stimulation does not influence the pool of neurons responding to sciatic nerve in the caudate nucleus. On the other hand, the cerebral peduncles exert an inhibitory action on such activity.