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.