title: (+)-Morphine attenuates the (-)-morphine-produced tail-flick inhibition via the sigma-1 receptor in the mouse spinal cord.
abstract: OBJECTIVE
  We have previously demonstrated that pretreatment with (+)-morphine given intrathecally attenuates the intrathecal (-)-morphine-produced tail-flick inhibition. The phenomenon has been defined as antianalgesia against (-)-morphine-produced analgesia. Present experiments were then undertaken to determine if the antianalgesic effect induced by (+)-morphine given spinally is mediated by the stimulation of the sigma-1 receptor in the mouse spinal cord.
  
  
  METHODS
  Sigma-1 receptor ligands, N-[2-(3,4-Dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine dihydrobromide (BD1047) and (+)-pentazocine were used to determine if (+)-morphine-induced antianalgesia is mediated by the stimulation of sigma-1 receptors in the mouse spinal cord. Tail-flick test was employed to measure the nociceptive response. All compounds were given intrathecally.
  
  
  RESULTS
  Pretreatment with BD1047 (1-10 μg) or (+)-pentazocine (0.1-10 μg) dose-dependently reversed the attenuation of the (-)-morphine-produced tail-flick inhibition induced by (+)-morphine (10 pg). BD1047 and (+)-pentazocine injected alone did not affect (-)-morphine-produced tail-flick inhibition.
  
  
  CONCLUSIONS
  The finding indicates that (+)-morphine attenuates the (-)-morphine-produced tail-flick inhibition via the activation of the sigma-1 receptors in the mouse spinal cord. Sigma-1 receptors may play an important role in opioid analgesia in the mouse spinal cord.
authors: Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
authors: Leon F
authors: LF
authors: Tseng
authors: Quinn H
authors: QH
authors: Hogan
authors: Hsiang-En
authors: HE
authors: Wu
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D005029:Ethylenediamines / Q000494:pharmacology; D008297:Male; D051379:Mice; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology; D059225:Nociception / Q000187:drug effects / Q000502:physiology; D010147:Pain Measurement / Q000187:drug effects*; D010423:Pentazocine / Q000494:pharmacology; D011930:Reaction Time / Q000187:drug effects; D017480:Receptors, sigma / Q000187:drug effects* / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects* / Q000502:physiology; D013623:Tail; D000097605:Sigma-1 Receptor
chemical_list: D000701:Analgesics, Opioid; D005029:Ethylenediamines; D009020:Morphine; D009292:Narcotic Antagonists; D010423:Pentazocine; D017480:Receptors, sigma; D000097605:Sigma-1 Receptor; C097963:N-(2-(3,4-Dichlorphenyl)ethyl)-N,N',N'-trimethyl-1,2-ethandiamin