Dorsal horn substance P and NK1 receptors: Study of a model system in spinal nociceptive processing

Abstract

Small unmyelinated fibers are the primary afferents by which input initiated by high intensity thermal and mechanical stimuli or by chemical products generated secondary to tissue injury, is communicated to the spinal cord. Events which increase small afferent terminal excitability and neurotransmitter release enhance the nociceptive message, while events which diminish small afferent terminal excitability/release diminish the magnitude of the post-synaptic depolarization and attenuate the pain message. The regulation of the activity of small afferent terminals which contain and release SP at the spinal level can be reasonably interpreted as representing effects (direct or indirect) on this family of peptidergic C-fiber terminals. Thus, SP release provides a well-defined model system for characterizing modulatory components involved in the in vivo regulation of pain behavior at this critical first order link.