title: Glial cell line-derived neurotrophic factor-mediated enhancement of noradrenergic descending inhibition in the locus coeruleus exerts prolonged analgesia in neuropathic pain.
abstract: OBJECTIVE
  The locus coeruleus (LC) is the principal nucleus containing the noradrenergic neurons and is a major endogenous source of pain modulation in the brain. Glial cell line-derived neurotrophic factor (GDNF), a well-established neurotrophic factor for noradrenergic neurons, is a major pain modulator in the spinal cord and primary sensory neurons. However, it is unknown whether GDNF is involved in pain modulation in the LC.
  
  
  METHODS
  Rats with chronic constriction injury (CCI) of the left sciatic nerve were used as a model of neuropathic pain. GDNF was injected into the left LC of rats with CCI for 3 consecutive days and changes in mechanical allodynia and thermal hyperalgesia were assessed. The α2 -adrenoceptor antagonist yohimbine was injected intrathecally to assess the involvement of descending inhibition in GDNF-mediated analgesia. The MEK inhibitor U0126 was used to investigate whether the ERK signalling pathway plays a role in the analgesic effects of GDNF.
  
  
  RESULTS
  Both mechanical allodynia and thermal hyperalgesia were attenuated 24 h after the first GDNF injection. GDNF increased the noradrenaline content in the dorsal spinal cord. The analgesic effects continued for at least 3 days after the last injection. Yohimbine abolished these effects of GDNF. The analgesic effects of GDNF were partly, but significantly, inhibited by prior injection of U0126 into the LC.
  
  
  CONCLUSIONS
  GDNF injection into the LC exerts prolonged analgesic effects on neuropathic pain in rats by enhancing descending noradrenergic inhibition.
authors.affiliation: Department of Anesthesiology, Graduate School of Medicine, Nippon Medical School, Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kimura
authors.forename: A
authors.initials: A
authors.lastname: Sakai
authors.forename: A
authors.initials: A
authors.lastname: Sakamoto
authors.forename: H
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D059331:Adrenergic Neurons / Q000187:drug effects* / Q000502:physiology; D058669:Adrenergic alpha-2 Receptor Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000700:Analgesics / Q000494:pharmacology / Q000627:therapeutic use*; D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use*; D006930:Hyperalgesia / Q000188:drug therapy / Q000503:physiopathology; D007278:Injections, Spinal; D008125:Locus Coeruleus / Q000187:drug effects* / Q000503:physiopathology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D008845:Microinjections; D009437:Neuralgia / Q000188:drug therapy* / Q000503:physiopathology; D009570:Nitriles / Q000494:pharmacology; D051381:Rats; D012584:Sciatic Nerve / Q000293:injuries; D015016:Yohimbine / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D058669:Adrenergic alpha-2 Receptor Antagonists; D000700:Analgesics; D002070:Butadienes; D004791:Enzyme Inhibitors; D051100:Glial Cell Line-Derived Neurotrophic Factor; D009570:Nitriles; C113580:U 0126; D015016:Yohimbine