NK-1 receptors in the rostral ventromedial medulla contribute to hyperalgesia produced by intraplantar injection of capsaicin

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27 Scopus citations

Abstract

The rostral ventromedial medulla (RVM) is an area of the brainstem involved in the descending modulation of nociception at the level of the spinal cord. Although the RVM is involved in the inhibition or facilitation of nociception, the underlying mechanisms are not understood. Here we examined the role of the neuropeptide substance P and neurokinin-1 (NK-1) receptors located in the RVM on withdrawal responses evoked by mechanical and heat stimuli applied to the rat hindpaw under normal conditions and during hyperalgesia produced by capsaicin. The mechanical withdrawal threshold was obtained using von Frey monofilaments applied to the plantar surface of the hindpaw. Sensitivity to heat was determined by measuring the latency to withdrawal from radiant heat applied to the plantar surface. Mechanical and heat hyperalgesia were defined as a decrease in withdrawal response threshold or latency, respectively. Rats were prepared with a chronic cannula and either vehicle or the NK-1 receptor antagonists, L-733,060 or RP-67580, was injected into the RVM. Paw withdrawal responses were obtained before and after RVM injection, and then at 5, 30, and 60 min after an intraplantar injection of capsaicin (10 μg). Injection of the NK-1 antagonists at doses of 0.5 pmol or higher did not alter withdrawal responses to mechanical or heat stimuli under normal conditions but reduced the duration of nocifensive behavior and the mechanical and heat hyperalgesia produced by capsaicin. These findings suggest that the activation of NK-1 receptors in the RVM contributes to the hyperalgesia produced by capsaicin.

Original languageEnglish (US)
Pages (from-to)34-46
Number of pages13
JournalPain
Volume139
Issue number1
DOIs
StatePublished - Sep 30 2008

Bibliographical note

Funding Information:
This study was supported by NIH Grants CA091007 and DA11471 (DAS). We want to thank Dr. Thaddeus Brink for reading an earlier version of the manuscript, and Dr. Thomas Fletcher for helping prepare the figures. The authors do not have any conflicts of interest related to this work.

Keywords

  • Brainstem
  • Descending facilitation
  • Pain
  • Substance P

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