Chronic effects of topical application of capsaicin to the sciatic nerve on responses of primate spinothalamic neurons

Jin Chung, K. S. Paik, J. S. Kim, S. C. Nam, K. J. Kim, U. T. Oh, T. Hasegawa, K. Chung, W. D. Willis

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The responses of 144 spinothalamic tract (STT) cells were recorded in 15 anesthetized macaque monkeys (Macaco fascicularis). Three to 4 weeks prior to the acute experiment, the sciatic nerve was surgically exposed on one or both sides so that capsaicin or vehicle could be applied. Responses of STT cells recorded in 3 experimental groups were compared: untreated (21 cells), vehicle-treated (40 cells), and capsaicin-treated (83 cells). The background activity of cells in the vehicle- and capsaicin-treated groups was the same as in the untreated group (that is, cells on the side contralateral to surgery). Responses to innocuous (BRUSH) and noxious (PINCH) mechanical stimuli were unchanged by vehicle or by capsaicin treatment. However, responses to other noxious (PRESSURE and SQUEEZE) mechanical stimuli were significantly increased in the vehicle-treated group. Compared with a large reference population, all experimental groups showed a significant increase in overall responsiveness to mechanical stimuli (as determined by cluster analysis), greatest in the vehicle-treated group. Responses to noxious heat stimuli were significantly reduced in the capsaicin-treated group for 45°C and 47°C stimuli. Volleys in A fibers, probably Aδ fibers, evoked prolonged responses in many STT cells of all treatment groups. Electron microscopic counts of axons in the sciatic nerves of animals treated with capsaicin showed a reduced number of C fibers but no appreciable loss of myelinated axons. This loss of unmyelinated sensory fibers was presumably responsible for the reduction in the responses of the STT cells to noxious heat stimuli. Increased responses to some noxious mechanical stimuli and to A fiber volleys may have been the consequence of several factors, including surgical manipulation, a chemical action of vehicle and a contralateral action of capsaicin treatment.

Original languageEnglish (US)
Pages (from-to)311-321
Number of pages11
JournalPain
Volume53
Issue number3
DOIs
StatePublished - 1993
Externally publishedYes

Fingerprint

Capsaicin
Sciatic Nerve
Primates
Spinothalamic Tracts
Neurons
Myelinated Nerve Fibers
Axons
Hot Temperature
Pharmacologic Actions
Unmyelinated Nerve Fibers
Macaca
Haplorhini
Cluster Analysis
Electrons

Keywords

  • Cluster analysis
  • Hyperalgesia
  • Noxious thermal stimuli
  • Unmyelinated fibers

ASJC Scopus subject areas

  • Clinical Neurology
  • Psychiatry and Mental health
  • Neuroscience(all)
  • Neurology
  • Pharmacology
  • Clinical Psychology

Cite this

Chronic effects of topical application of capsaicin to the sciatic nerve on responses of primate spinothalamic neurons. / Chung, Jin; Paik, K. S.; Kim, J. S.; Nam, S. C.; Kim, K. J.; Oh, U. T.; Hasegawa, T.; Chung, K.; Willis, W. D.

In: Pain, Vol. 53, No. 3, 1993, p. 311-321.

Research output: Contribution to journalArticle

Chung, J, Paik, KS, Kim, JS, Nam, SC, Kim, KJ, Oh, UT, Hasegawa, T, Chung, K & Willis, WD 1993, 'Chronic effects of topical application of capsaicin to the sciatic nerve on responses of primate spinothalamic neurons', Pain, vol. 53, no. 3, pp. 311-321. https://doi.org/10.1016/0304-3959(93)90227-G
Chung, Jin ; Paik, K. S. ; Kim, J. S. ; Nam, S. C. ; Kim, K. J. ; Oh, U. T. ; Hasegawa, T. ; Chung, K. ; Willis, W. D. / Chronic effects of topical application of capsaicin to the sciatic nerve on responses of primate spinothalamic neurons. In: Pain. 1993 ; Vol. 53, No. 3. pp. 311-321.
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AU - Chung, Jin

AU - Paik, K. S.

AU - Kim, J. S.

AU - Nam, S. C.

AU - Kim, K. J.

AU - Oh, U. T.

AU - Hasegawa, T.

AU - Chung, K.

AU - Willis, W. D.

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AB - The responses of 144 spinothalamic tract (STT) cells were recorded in 15 anesthetized macaque monkeys (Macaco fascicularis). Three to 4 weeks prior to the acute experiment, the sciatic nerve was surgically exposed on one or both sides so that capsaicin or vehicle could be applied. Responses of STT cells recorded in 3 experimental groups were compared: untreated (21 cells), vehicle-treated (40 cells), and capsaicin-treated (83 cells). The background activity of cells in the vehicle- and capsaicin-treated groups was the same as in the untreated group (that is, cells on the side contralateral to surgery). Responses to innocuous (BRUSH) and noxious (PINCH) mechanical stimuli were unchanged by vehicle or by capsaicin treatment. However, responses to other noxious (PRESSURE and SQUEEZE) mechanical stimuli were significantly increased in the vehicle-treated group. Compared with a large reference population, all experimental groups showed a significant increase in overall responsiveness to mechanical stimuli (as determined by cluster analysis), greatest in the vehicle-treated group. Responses to noxious heat stimuli were significantly reduced in the capsaicin-treated group for 45°C and 47°C stimuli. Volleys in A fibers, probably Aδ fibers, evoked prolonged responses in many STT cells of all treatment groups. Electron microscopic counts of axons in the sciatic nerves of animals treated with capsaicin showed a reduced number of C fibers but no appreciable loss of myelinated axons. This loss of unmyelinated sensory fibers was presumably responsible for the reduction in the responses of the STT cells to noxious heat stimuli. Increased responses to some noxious mechanical stimuli and to A fiber volleys may have been the consequence of several factors, including surgical manipulation, a chemical action of vehicle and a contralateral action of capsaicin treatment.

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KW - Noxious thermal stimuli

KW - Unmyelinated fibers

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