Dorsal root potentials after C-fiber stimulation.

A pure volley from C-fibers, set up by electrical stimulation of a cutaneous nerve and subsequent selective blocking of the A-fibers, generates in the cat spinal cord a dorsal root potential (C-DRP). Its polarity is the same as that of the dorsal root potential elicited by stimulation of the A-fibers (A-DRP), thus probably providing presynaptic inhibition of primary afferents. The size of the C-DRP increases in proportion to the size of the C-volley. A preceding A-DRP reduces the C-DRP.