Modulation of peripheral endogenous opioid analgesia by central afferent blockade
Male; Analgesics; Animals; Rats; Injections; Immunohistochemistry; Spinal; Enkephalin; beta-Endorphin/metabolism; Wistar; Pain Threshold/drug effects; Neurons; Afferent/drug effects; Central Nervous System/drug effects; Endorphins/metabolism/physiology; Flow Cytometry; Foot/pathology; Inflammation/pathology; Methionine/metabolism; Morphine/administration & dosage/pharmacology; Opioid/administration & dosage/pharmacology; Peripheral Nerves/drug effects; Psychomotor Performance/drug effects
BACKGROUND: Peripheral tissue injury causes a migration of opioid peptide-containing immune cells to the inflamed site. The subsequent release and action of these peptides on opioid receptors localized on peripheral sensory nerve terminals causes endogenous analgesia. The spinal application of opioid drugs blocks the transmission of nociceptive information from peripheral injury. This study investigates the influence of exogenous spinal opioid analgesia on peripheral endogenous opioid analgesia. METHODS: Six and forty-eight hours after initiation of continuous intrathecal morphine infusion and administration of Freund's complete adjuvant into the hind paw of rats, antinociceptive and antiinflammatory effects were measured by paw pressure threshold, paw volume, and paw temperature, respectively. Inflammation and quantity of opioid-containing cells were evaluated by immunocytochemistry and flow cytometry. Cold water swim stress-induced endogenous analgesia was examined 24 h after discontinuation of intrathecal morphine administration. RESULTS: Intrathecal morphine (10 micro g/h) resulted in a significant and stable increase of paw pressure threshold ( P 0.05). At 48 but not at 6 h after Freund's complete adjuvant, the number of beta-endorphin-containing cells and cold water swim-induced antinociception were significantly reduced in intrathecal morphine-treated rats compared with those treated with intrathecal vehicle ( P< 0.05). CONCLUSIONS: These findings suggest an interplay of central and peripheral mechanisms of pain control. An effective central inhibition of pain apparently signals a reduced need for recruitment of opioid-containing immune cells to injured sites.
2003
Schmitt TK; Mousa SA; Brack A; Schmidt DK; Rittner HL; Welte M; Schafer M; Stein C
Anesthesiology
2003
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/10.1097/00000542-200301000-00030" target="_blank" rel="noreferrer">10.1097/00000542-200301000-00030</a>
Tissue monocytes/macrophages in inflammation: hyperalgesia versus opioid-mediated peripheral antinociception
Male; Analgesics; Animals; Rats; Biomarkers of Pain; Injections; Pain Measurement/drug effects; Freund's Adjuvant; Wistar; Flow Cytometry; Foot/pathology; Opioid/administration & dosage/pharmacology; Clodronic Acid/pharmacokinetics/pharmacology; Fentanyl/administration & dosage/pharmacology; Heat; Hyperalgesia/chemically induced/pathology/psychology; Inflammation/chemically induced/pathology; Liposomes; Macrophages/pathology; Monocytes/pathology; Non-Narcotic/pharmacokinetics/pharmacology; Pressure
BACKGROUND: Opioid-containing leukocytes migrate to peripheral sites of inflammation. On exposure to stress, opioid peptides are released, bind to opioid receptors on peripheral sensory neurons, and induce endogenous antinociception. In later stages of Freund's complete adjuvant-induced local inflammation, monocytes/macrophages are a major opioid-containing leukocyte subpopulation, but these cells also produce proalgesic cytokines. In this study, the role of tissue monocytes/macrophages in hyperalgesia and in peripheral opioid-mediated antinociception was investigated. METHODS: After intraplantar injection of Freund's adjuvant, leukocyte subpopulations and opioid-containing leukocytes were analyzed by flow cytometry in the inflamed paw in the presence or absence of monocyte/macrophage depletion by intraplantar injection of clodronate-containing liposomes (phosphate-buffered saline and empty liposomes served as controls). Paw volume was measured with a plethysmometer. Hyperalgesia was determined by measuring heat-induced paw withdrawal latency and paw pressure threshold. Paw pressure threshold was also measured after swim stress and injection of fentanyl. RESULTS: At 48 and 96 h of inflammation, it was found that (1). monocytes/macrophages were the largest leukocyte subpopulation (> 55% of all leukocytes) and the predominant producers of opioid peptides (71-77% of all opioid-containing leukocytes in the paw), (2). clodronate-containing liposomes depleted monocytes/macrophages by 30-35% (P 0.05), and (4) opioid-containing leukocytes and swim stress but not fentanyl-induced antinociception were significantly decreased by clodronate-containing liposomes (P 0.05, all by t test; opioid-containing cells and swim stress-induced increase of paw pressure threshold were reduced by 35-42% and 20%, respectively). CONCLUSION: Partial depletion of tissue monocytes/macrophages impairs peripheral endogenous opioid-mediated antinociception without affecting hyperalgesia.
2004
Brack A; Labuz D; Schiltz A; Rittner HL; Machelska H; Schafer M; Reszka R; Stein C
Anesthesiology
2004
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/10.1097/00000542-200407000-00031" target="_blank" rel="noreferrer">10.1097/00000542-200407000-00031</a>