Mechanical hyperalgesia after spinal nerve ligation in rat is not reversed by intraplantar or systemic administration of adrenergic antagonists

Matthias Ringkamp, Erich J. Grethel, Yoon Choi, Richard A. Meyer, Srinivasa N. Raja

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


The development of α-adrenergic sensitivity in cutaneous nociceptors has been postulated as a mechanism for sympathetically maintained pain (SMP). In order to characterize the adrenergic receptors involved, we investigated the effects of intraplantar administration of α1-(prazosin) and α2-(yohimbine) adrenergic antagonists and systemic injection of phentolamine, a non-specific α-adrenergic blocker, on allodynic/hyperalgesic behavior in an animal model thought to mimic SMP in humans. Peripheral neuropathy in rats was induced by tight ligation of the L5/L6 spinal nerves. Mechanical hyperalgesia was quantified with von Frey hairs applied either for 3 s or repetitively to the plantar surface of the hindpaw. Responses to the 3 s duration stimulus were used to determine the paw withdrawal threshold with the up-down paradigm and repetitive stimuli were used to determine the response incidence of paw withdrawal to a given von Frey hair. Mechanical thresholds on the ipsilateral paw decreased significantly after ligation and were stable over the following 3 weeks. Intradermal administration of yohimbine or prazosin did not significantly alleviate mechanical hyperalgesia in L5/L6 ligated animals. Also systemic administration of phentolamine (1 and 5 mg/kg) did not alleviate the increased incidence of paw withdrawal in L5/L6 spinal nerve ligated animals. These results suggest that an alpha adrenergic interaction between sympathetic efferent and somatic afferent fibers does not play a critical role for the maintenance of mechanical hyperalgesia in this model for neuropathic pain. Copyright (C) 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.

Original languageEnglish (US)
Pages (from-to)135-141
Number of pages7
Issue number2-3
StatePublished - Feb 1 1999


  • L5 ligation
  • Neuropathic pain
  • Sympathetically maintained pain

ASJC Scopus subject areas

  • Neurology
  • Clinical Neurology
  • Anesthesiology and Pain Medicine


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