Chemical Excitation and Sensitization of Nociceptors

Abstract

Sensory capacities of nociceptors have been extensively characterised using noxious mechanical and thermal stimuli. Apart from interesting exceptions, nociceptor responsiveness correlated reasonably well with human sensation or animal behavior.¹ These sensory capacities, however, fail to explain pain that outlasts the acute injury, e.g. post traumatic and inflammatory pain, or pain that results from harmless physical actions as in the case of hyperalgesia. To understand the ongoing discharge and sensitization of nociceptors in these conditions, it is necessary to know about chemical influences on the peripheral nerve endings. This knowledge has been considerably advanced by the introduction of in vitro techniques in primary afferent physiology.^2,4,11,18 In our hands, it is a superfused rat skin-nerve preparation that provides differentiated and well categorised populations of cutaneous nociceptors and allows treatment of their receptive fields directly with chemicals in controlled concentrations. The following data in this brief review result from a number of studies on this preparation using the single fiber recording method.