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Spinal Endocannabinoids and CB1 Receptors Mediate C-Fiber–Induced Heterosynaptic Pain Sensitization

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Science  07 Aug 2009:
Vol. 325, Issue 5941, pp. 760-764
DOI: 10.1126/science.1171870

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Plastic Pain Perception

Drugs and endocannabinoids acting on cannabinoid (CB) receptors have potential in the treatment of certain types of pain. In the spinal cord they are believed to suppress nociception, the perception of pain and noxious stimuli. Pernia-Andrade et al. (p. 760) now find that endocannabinoids, which are released in spinal cord by noxious stimulation, may promote rather than inhibit nociception by acting on CB1 receptors. Endocannabinoids not only depress transmission at excitatory synapses in the spinal cord, but also block the release of inhibitory neurotransmitters, thereby facilitating nociception.

Abstract

Diminished synaptic inhibition in the spinal dorsal horn is a major contributor to chronic pain. Pathways that reduce synaptic inhibition in inflammatory and neuropathic pain states have been identified, but central hyperalgesia and diminished dorsal horn synaptic inhibition also occur in the absence of inflammation or neuropathy, solely triggered by intense nociceptive (C-fiber) input to the spinal dorsal horn. We found that endocannabinoids, produced upon strong nociceptive stimulation, activated type 1 cannabinoid (CB1) receptors on inhibitory dorsal horn neurons to reduce the synaptic release of γ-aminobutyric acid and glycine and thus rendered nociceptive neurons excitable by nonpainful stimuli. Our results suggest that spinal endocannabinoids and CB1 receptors on inhibitory dorsal horn interneurons act as mediators of heterosynaptic pain sensitization and play an unexpected role in dorsal horn pain-controlling circuits.

  • * These authors contributed equally to this work.

  • Present address: Institute of Physiology, University of Freiburg, Engesserstrasse 4, D-79108, Freiburg, Germany.

  • Present address: Department of Anesthesiology, Medical School Hannover, D-30625 Hannover, Germany.

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