Chapter 10 The possible role of substance P in eliciting and modulating deep somatic pain

Abstract

This chapter focuses on the results and discussions concerning the involvement of substance P (SP) in the mediation of deep somatic pain (from muscle, fascia, tendon, and joint). SP-related events in skeletal muscle and spinal cord are addressed. The physiological function of the SP- and calcitonin gene-related peptide (CGRP)-ir fibres that exhibited an increase in numerical density is unknown. If the effect is present also in nociceptors, pain sensations from an inflamed muscle could be due not only to an increased discharge activity in these endings but also to a recruitment of active nociceptive endings. This latter effect could lead to an enhancement of pain because of an increased spatial summation at the first synapses in the spinal cord. The chapter presents only the neurones that had no mechanosensitive receptive fields (RFs) in the skin. No information is available concerning a possible relationship between functional properties and type of SP effect. It is likely, however, that such a relationship exists, because in nociceptive neurones the only SP effect observed is an increase in RF size or number of RFs. Whether all nociceptive neurones react to SP in this way is unknown.