Physiological Society Symposium - Nociceptors as Homeostatic Afferents: Central Processing
Phenotype and function of somatic primary afferent nociceptive neurones with C-, A[delta]- or A[alpha]/[beta]-fibres
Nociceptive dorsal root ganglion (DRG) neurones have fibres that conduct in the C, A[delta] and A[alpha]/[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, A[delta] or A[alpha]/[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 A[delta]-fibres and least pronounced in those with A[alpha]/[beta] fibres (C > A[delta] > A[alpha]/[beta]). Some of these properties are also expressed in a less extreme but similarly graded manner through C, A[delta] and A[alpha]/[beta] groups of non-nociceptive low threshold mechanoreceptive (LTM) neurone. The less common pattern B properties of nociceptive neurones have similar values in C-, A[delta]- and A[alpha]/[beta]-fibre nociceptive neurones but these clearly differ from LTM units with C-, A[delta]- and A[alpha]/[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. Experimental Physiology (2002) 87.2, 239-244.