title: Itch and analgesia resulting from intrathecal application of morphine: contrasting effects on different populations of trigeminothalamic tract neurons.
abstract: Intrathecal application of morphine is among the most powerful methods used to treat severe chronic pain. However, this approach commonly produces itch sufficiently severe that patients are forced to choose between relief of pain or itch. The neuronal populations responsible for processing and transmitting information underlying itch caused by intrathecal application of morphine have not been identified and characterized. We describe two populations of antidromically identified trigeminothalamic tract (VTT) neurons in anesthetized rats that are differentially affected by morphine and explain several aspects of opioid-induced itch and analgesia. We found that intrathecal application of morphine increased ongoing activity of itch-responsive VTT neurons. In addition, intrathecal application of morphine increased responses to pruritogens injected into the skin and greatly heightened responses to innocuous mechanical stimuli. In contrast, the ongoing activity and responses to noxious pinches in nociceptive VTT neurons were frequently inhibited by the same dose of morphine. These results reveal that i.t. application of morphine affects specific subpopulations of VTT neurons in ways that may produce itch, hyperknesis, alloknesis, and analgesia.
authors.affiliation: Graduate Program in Neuroscience and Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota, 55455, USA.
authors.forename: Hannah R
authors.initials: HR
authors.lastname: Moser
authors.forename: Glenn J
authors.initials: GJ
authors.lastname: Giesler
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000009:adverse effects*; D000818:Animals; D018501:Antirheumatic Agents / Q000494:pharmacology; D002738:Chloroquine / Q000494:pharmacology; D004558:Electric Stimulation; D006632:Histamine / Q000494:pharmacology; D007278:Injections, Spinal / Q000379:methods; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000009:adverse effects*; D009434:Neural Pathways / Q000187:drug effects*; D010146:Pain / Q000188:drug therapy*; D010446:Peptide Fragments / Q000494:pharmacology; D011537:Pruritus / Q000139:chemically induced*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology; D013268:Stimulation, Chemical; D013788:Thalamus / Q000166:cytology* / Q000293:injuries; D014278:Trigeminal Nuclei / Q000166:cytology* / Q000293:injuries
chemical_list: D000701:Analgesics, Opioid; D018501:Antirheumatic Agents; D010446:Peptide Fragments; C571042:bovine adrenal medulla 8-22; D012701:Serotonin; D009020:Morphine; D006632:Histamine; D002738:Chloroquine
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