Spatial properties of nociceptor sensitization following heat injury of the skin.

A brief noxious heat stimulus applied to half of the receptive field of each cutaneous nociceptor resulted in most cases in the enhanced responsiveness of that half to subsequent heat stimuli (sensitization). No change in responsiveness to heat was observed in the other half of the receptive field, indicating that the effects of heat sensitization did not spread from the site of injury. In certain instances, the receptive field area increased, but the enlargement occurred only within the area of injury. The latter suggests the existence of outlying terminal endings of the parent axon that are normally unresponsive to non-injurious mechanical or heat stimuli but become responsive to these stimuli following injury.