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Activity-dependent slowing of conduction velocity provides a method for identifying different functional classes of C-fibre in the rat saphenous nerve.
Neuroscience. 1996 Aug; 73(3):667-75.N

Abstract

Repetitive firing of nerve fibres results in the slowing of their conduction velocity. The extent of conduction velocity slowing throughout a standard electrical stimulus (20 s, 20 Hz, 2 x electrical threshold) was examined in identified C-fibres dissected from the saphenous nerve of anaesthetized rats. The aim of this study was to establish whether the different functional classes of C-fibre could be identified on the basis of their activity-dependent slowing of conduction velocity. Following 20 s of stimulation at 20 Hz, nociceptive C-fibres showed a significantly greater slowing of conduction velocity (mean +/- S.E.; polymodal and heat nociceptors = 29.2% +/- 0.7, n = 53; mechanical nociceptors = 27.7% +/- 1.7, n =13) than cold thermoreceptive fibres (10.8% +/- 0.6, n = 10), mechanoreceptors (14.4% +/- 0.8, n = 17) and spontaneously active sympathetic efferent units (14.9% +/- 0.8, n = 24). The degree of conduction velocity slowing shown by a unit was not correlated with its resting conduction velocity. There was little overlap of the degree of conduction velocity slowing between the nociceptive and non-nociceptive fibres. Also, there was little overlap of conduction velocity slowing between the mechanoreceptors and the cold units, particularly after just 6 s of stimulation at 20 Hz. Units for which no receptive field to mechanical or thermal stimuli could be found showed a bimodal distribution of conduction velocity slowing. In the saphenous nerve, such inexcitable units will be of three main types--sympathetic efferent units, "sleeping" or "silent" nociceptors and non-cutaneous afferent fibres. Those inexcitable units slowing in conduction velocity by greater than 20% showed a similar distribution to the polymodal nociceptors and those inexcitable units slowing by less than 20% showed a similar distribution to the spontaneously active sympathetic units. Twenty-three of the 61 units without mechanical or thermal receptive fields were investigated using electrical skin stimulation and topical application of 5 or 10% mustard oil. Afferent fields could not be found for any of the nine units that slowed in conduction velocity by less than 20%. Afferent fields were detected for 11 of the remaining 14 insensitive units, which all showed a greater than 20% slowing from resting conduction velocity. Therefore, one can distinguish nociceptive and non-nociceptive afferent fibres simply by looking at the axonal property of activity-dependent slowing of conduction velocity. Moreover, it is possible to use this axonal property to separate the two classes of non-nociceptive afferent C-fibre (i.e. mechanoreceptors and cold thermoreceptors). In addition, one can also use this parameter to differentiate between the afferent and non-afferent populations of inexcitable C-fibres. The ability to identify a particular fibre type on the basis of an axonal property provides a useful tool for the functional classification of fibres in experiments where axons are separated from their terminals.

Authors+Show Affiliations

Department of Physiology, University College London, U.K.No affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

8809788

Citation

Gee, M D., et al. "Activity-dependent Slowing of Conduction Velocity Provides a Method for Identifying Different Functional Classes of C-fibre in the Rat Saphenous Nerve." Neuroscience, vol. 73, no. 3, 1996, pp. 667-75.
Gee MD, Lynn B, Cotsell B. Activity-dependent slowing of conduction velocity provides a method for identifying different functional classes of C-fibre in the rat saphenous nerve. Neuroscience. 1996;73(3):667-75.
Gee, M. D., Lynn, B., & Cotsell, B. (1996). Activity-dependent slowing of conduction velocity provides a method for identifying different functional classes of C-fibre in the rat saphenous nerve. Neuroscience, 73(3), 667-75.
Gee MD, Lynn B, Cotsell B. Activity-dependent Slowing of Conduction Velocity Provides a Method for Identifying Different Functional Classes of C-fibre in the Rat Saphenous Nerve. Neuroscience. 1996;73(3):667-75. PubMed PMID: 8809788.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Activity-dependent slowing of conduction velocity provides a method for identifying different functional classes of C-fibre in the rat saphenous nerve. AU - Gee,M D, AU - Lynn,B, AU - Cotsell,B, PY - 1996/8/1/pubmed PY - 1996/8/1/medline PY - 1996/8/1/entrez SP - 667 EP - 75 JF - Neuroscience JO - Neuroscience VL - 73 IS - 3 N2 - Repetitive firing of nerve fibres results in the slowing of their conduction velocity. The extent of conduction velocity slowing throughout a standard electrical stimulus (20 s, 20 Hz, 2 x electrical threshold) was examined in identified C-fibres dissected from the saphenous nerve of anaesthetized rats. The aim of this study was to establish whether the different functional classes of C-fibre could be identified on the basis of their activity-dependent slowing of conduction velocity. Following 20 s of stimulation at 20 Hz, nociceptive C-fibres showed a significantly greater slowing of conduction velocity (mean +/- S.E.; polymodal and heat nociceptors = 29.2% +/- 0.7, n = 53; mechanical nociceptors = 27.7% +/- 1.7, n =13) than cold thermoreceptive fibres (10.8% +/- 0.6, n = 10), mechanoreceptors (14.4% +/- 0.8, n = 17) and spontaneously active sympathetic efferent units (14.9% +/- 0.8, n = 24). The degree of conduction velocity slowing shown by a unit was not correlated with its resting conduction velocity. There was little overlap of the degree of conduction velocity slowing between the nociceptive and non-nociceptive fibres. Also, there was little overlap of conduction velocity slowing between the mechanoreceptors and the cold units, particularly after just 6 s of stimulation at 20 Hz. Units for which no receptive field to mechanical or thermal stimuli could be found showed a bimodal distribution of conduction velocity slowing. In the saphenous nerve, such inexcitable units will be of three main types--sympathetic efferent units, "sleeping" or "silent" nociceptors and non-cutaneous afferent fibres. Those inexcitable units slowing in conduction velocity by greater than 20% showed a similar distribution to the polymodal nociceptors and those inexcitable units slowing by less than 20% showed a similar distribution to the spontaneously active sympathetic units. Twenty-three of the 61 units without mechanical or thermal receptive fields were investigated using electrical skin stimulation and topical application of 5 or 10% mustard oil. Afferent fields could not be found for any of the nine units that slowed in conduction velocity by less than 20%. Afferent fields were detected for 11 of the remaining 14 insensitive units, which all showed a greater than 20% slowing from resting conduction velocity. Therefore, one can distinguish nociceptive and non-nociceptive afferent fibres simply by looking at the axonal property of activity-dependent slowing of conduction velocity. Moreover, it is possible to use this axonal property to separate the two classes of non-nociceptive afferent C-fibre (i.e. mechanoreceptors and cold thermoreceptors). In addition, one can also use this parameter to differentiate between the afferent and non-afferent populations of inexcitable C-fibres. The ability to identify a particular fibre type on the basis of an axonal property provides a useful tool for the functional classification of fibres in experiments where axons are separated from their terminals. SN - 0306-4522 UR - https://www.unboundmedicine.com/medline/citation/8809788/Activity_dependent_slowing_of_conduction_velocity_provides_a_method_for_identifying_different_functional_classes_of_C_fibre_in_the_rat_saphenous_nerve_ L2 - https://linkinghub.elsevier.com/retrieve/pii/0306-4522(96)00070-X DB - PRIME DP - Unbound Medicine ER -