RESPONSES OF SINGLE DORSAL CORD CELLS TO PERIPHERAL CUTANEOUS UNMYELINATED FIBRES.

Abstract

IN the dorsal part of the dorsal horn there is a lamina of cells which respond to cutaneous stimulation and send their axons into the dorsolateral tract. In previous investigations1 it was apparent that many different types of A fibres converged on these cells. It is, therefore, interesting to see whether C fibres also affect their firing. In a recent investigation2 it was found that an afferent volley in the unmyelinated fibres led to a positive dorsal root potential as opposed to the well-known negative dorsal potential which is elicited by the large myelinated fibres. It was suggested that C fibres led to presynaptic hyperpolarization which would produce facilitation as contrasted with the presynaptic inhibitory effects of the A fibres. An investigation of the ventral root reflex (VRR, ref. 2) showed no late component which could be attributed to C fibres; however, a tetanus in the C's was found to potentiate the VRR elicited by the A fibres in the same peripheral nerve. It was also known that a large stimulus to a peripheral nerve led to late discharges in various midbrain and forebrain structures3. With these factors in mind an investigation of the response of cells in the dorsolateral tract of the cat to C fibres was carried out.