Presynaptic Inhibition

Abstract

Gasser and Graham (1933) found that dorsal root volleys produced slow positive potentials (P waves) of the cord dorsum, and that the time courses of these waves corresponded approximately to that of the inhibition of flexor reflexes when one dorsal root volley was employed to condition the flexor reflex evoked by another volley. Consequently, they asked “whether the positive potential may not be connected with the process responsible for inhibition?”. In further communications Hughes and Gasser (1934a, 1934b) provided additional evidence supporting this correlation; and later Gasser (1937) attributed the inhibition to a depression of interneurones in a common central pathway that was produced by the positive after-potential that followed their activation by the conditioning volley. Barron and Matthews (1938) found that dorsal root volleys also gave rise to a depolarization that spread electrotonically along the same or adjacent dorsal roots and postulated that this dorsal root potential (DRP) was produced by the same potential generator that gave the P wave; and this identification has been accepted by all subsequent investigators (Bremer and Bonnet 1942; Bernhard 1952, 1953; Koketsu 1956a, 1956b; Eccles, Magni and Willis 1962; Eccles, Kostyuk and Schmidt 1962a; Eccles, Schmidt and Willis 1963a, 1963b).