A Morphological Basis for Pre-synaptic Inhibition?

Abstract

IN the past, several workers have suggested that central inhibitory action may occur in the pre-synaptic pathway by a block or depression of the pre-synaptic impulse. Observations, which could be interpreted in this way, were reported by Frank and Fuortes¹, who described a diminution in the excitatory post-synaptic potential produced in motoneurones by muscle afferents, accompanied by no other change in the resting potential of the motoneurone. Eccles² and others have produced more conclusive evidence for pre-synaptic inhibition; for example, it would appear that in the spinal cord the afferent axons from annulospiral endings (Group 1a) and Golgi tendon organs (Group 1b) depolarize (by a chemical transmitter) nearby terminals of the spindle afferents via interneurones, reducing the size of their pre-synaptic impulse and hence the amount of their excitatory transmitter substance liberated.