Phenotype and function of somatic primary afferent nociceptive neurones with C-, Adelta- or Aalpha/beta-fibres.
Nociceptive dorsal root ganglion (DRG) neurones have fibres that conduct in the C, Adelta and Aalpha/beta conduction velocity range. The properties of nociceptive compared with non-nociceptive somatic afferent dorsal root ganglion neurones appear to fall into two patterns, A and B. Pattern A properties of nociceptive neurones, the more common type, include longer action potential duration and slower maximum rate of fibre firing, as well as a greater expression of substance P and calcitonin gene-related peptide immunoreactivity. The values of pattern A properties appear to be graded according to the conduction velocity group (C, Adelta or Aalpha/beta) of the fibres. The most pronounced forms of A-type properties are expressed by nociceptive neurones with C-fibres, and these become less pronounced in nociceptive neurones with Adelta-fibres and least pronounced in those with Aalpha/beta fibres (C > Adelta > Aalpha/beta). Some of these properties are also expressed in a less extreme but similarly graded manner through C, Adelta and Aalpha/beta groups of non-nociceptive low threshold mechanoreceptive (LTM) neurone. The less common pattern B properties of nociceptive neurones have similar values in C-, Adelta- and Aalpha/beta-fibre nociceptive neurones but these clearly differ from LTM units with C-, Adelta- and Aalpha/beta-fibre conduction velocities. These features of nociceptive neurones include consistently larger action potential overshoots and longer after-hyperpolarisation durations in nociceptive than in LTM neurones.
Lawson
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Department of Physiology, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK. sally.lawson@bristol.ac.uk
D000818:Animals; D005727:Ganglia, Spinal / Q000166:cytology / Q000502:physiology; D006801:Humans; D009412:Nerve Fibers / Q000502:physiology*; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology* / Q000648:ultrastructure; D009619:Nociceptors / Q000502:physiology* / Q000648:ultrastructure; D010641:Phenotype