Inhibition of inflammatory pain by CRF at peripheral, spinal and supraspinal sites: involvement of areas coexpressing CRF receptors and opioid peptides
Male; Pain Measurement; Animals; Rats; Biomarkers of Pain; Dose-Response Relationship; Drug; Receptors; Freund's Adjuvant; Wistar; Animal; Disease Models; Analgesics/administration & dosage; Drug Administration Routes; Pain Threshold/drug effects; Brain/drug effects/metabolism; Spinal Cord/drug effects/metabolism; Corticotropin-Releasing Hormone/administration & dosage; Opioid Peptides/metabolism; Corticotropin-Releasing Hormone/metabolism; Ganglia; Hormone Antagonists/administration & dosage; Inflammation/chemically induced/complications; Pain/drug therapy/etiology/pathology; Sciatic Nerve/pathology; Spinal/drug effects/metabolism
There is conflicting evidence on the antinociceptive effects of corticotropin-releasing factor (CRF) along the neuraxis of pain transmission and the responsible anatomical sites of CRF's action at the level of the brain, spinal cord and periphery. In an animal model of tonic pain, that is, Freunds complete adjuvant (FCA) hindpaw inflammation, we systematically investigated CRF's ability to modulate inflammatory pain at those three levels of pain transmission by algesiometry following the intracerebroventricular, intrathecal, and intraplantar application of low, systemically inactive doses of CRF. At each level, CRF elicits potent antinociceptive effects, which are dose dependent and antagonized by local, but not systemic CRF receptor antagonist alpha-helical CRF indicating CRF receptor specificity. Consistently, we have identified by immunohistochemistry multiple brain areas, inhibitory interneurons within the dorsal horn of the spinal cord as well as immune cells within subcutaneous tissue--but not peripheral sensory neurons--that coexpress both CRF receptors and opioid peptides. In line with these anatomical findings, local administration of CRF together with the opioid receptor antagonist naloxone dose-dependently reversed CRF's antinociceptive effects at each of these three levels of pain transmission. Therefore, local application of low, systemically inactive doses of CRF at the level of the brain, spinal cord and periphery inhibits tonic inflammatory pain most likely through an activation of CRF receptors on cells that coexpress opioid peptides which results in opioid-mediated pain inhibition. Future studies have to delineate whether endogenous CRF at these three levels contributes to the body's response to cope with the stressful stimulus pain in an opioid-mediated manner.
2007
Mousa SA; Bopaiah CP; Richter JF; Yamdeu RS; Schafer M
Neuropsychopharmacology
2007
Article information provided for research and reference use only. PedPalASCNET does not hold any rights over the resource listed here. All rights are retained by the journal listed under publisher and/or the creator(s).
Journal Article
<a href="http://doi.org/10.1038/sj.npp.1301393" target="_blank" rel="noreferrer">10.1038/sj.npp.1301393</a>
Glia: novel counter-regulators of opioid analgesia
Humans; Analgesics; Animals; Opioid/administration & dosage; Drug Tolerance; Brain/drug effects/metabolism; Neuroglia/drug effects/metabolism; Neurotransmitter Agents/metabolism; Nociceptors/drug effects/metabolism; Pain/metabolism/prevention & control; Spinal Cord/drug effects/metabolism
Development of analgesic tolerance and withdrawal-induced pain enhancement present serious difficulties for the use of opioids for pain control. Although neuronal mechanisms to account for these phenomena have been sought for many decades, their bases remain unresolved. Within the past four years, a novel non-neuronal candidate has been uncovered that opposes acute opioid analgesia and contributes to development of opioid tolerance and tolerance-associated pain enhancement. This novel candidate is spinal cord glia. Glia are important contributors to the creation of enhanced pain states via the release of neuroexcitatory substances. New data suggest that glia also release neuroexcitatory substances in response to morphine, thereby opposing its effects. Controlling glial activation could therefore increase the clinical utility of analgesic drugs.
2005
Watkins LR; Hutchinson MR; Johnston IN; Maier SF
Trends In Neurosciences
2005
Article information provided for research and reference use only. PedPalASCNET does not hold any rights over the resource listed here. All rights are retained by the journal listed under publisher and/or the creator(s).
Journal Article
<a href="http://doi.org/10.1016/j.tins.2005.10.001" target="_blank" rel="noreferrer">10.1016/j.tins.2005.10.001</a>