Development of the nociceptor phenotype: role of nerve growth factor

The notion that specialized nociceptors exist among the afferent fibre population is a relatively recent one. Although indirect evidence for the existence of these fibres had been available for many years, it was not until much later that definitive single-unit studies revealed the presence of neurones selectively activated by stimuli that are potentially damaging to the skin. These studies in the cat clarified that there are two major groups of nociceptive afferents, one of which conducts in the Αδ conduction velocity range and the other of which conducts in the C-fibre range. The former are innervate receptors that are high-threshold mechanoreceptors (HTMs), whereas the latter are more diverse in their properties with many being sensitive to multiple modalities of stimulation (mechanical, thermal, chemical) giving rise to the name polymodal nociceptor. More recently, these two groups of fibres have been identified in the rat. This chapter focuses on the development of nociceptors, and particularly on the role of nerve growth factor (NGF) in determining the development of these sensory receptors.