Peripheral excitatory input to substantia nigra

Abstract In chloralose-anesthetized cats, unitary responses were recorded from the substantia nigra after electrical and natural stimulation of the extremities. Forty-eight nigral neurons from a total of 67 in the pars compacta as well as in the pars reticulata responded to electrical stimulation of either paws or dissected peripheral nerves with a latency of about 15 to 20 ms. Bilateral convergent responses were generally observed with some preferential side for a given neuron. It was revealed that electrical stimulation of the flexor nerve or cutaneous nerve was far more effective in inducing nigral response. It was also demonstrated that passive flexion of the forearm increased the spontaneous discharge whereas passive extension suppressed it. These nigral reponses to peripheral stimulation were still recorded after extensive lesion of the diencephalon, thus interrupting all nigral afferent fibers from higher centers. The functional role of the flexor afferent projection of the substantia nigra is discussed.