title: PI3K mediated activation of GSK-3β reduces at-level primary afferent growth responses associated with excitotoxic spinal cord injury dysesthesias.
abstract: BACKGROUND
  Neuropathic pain and sensory abnormalities are a debilitating secondary consequence of spinal cord injury (SCI). Maladaptive structural plasticity is gaining recognition for its role in contributing to the development of post SCI pain syndromes. We previously demonstrated that excitotoxic induced SCI dysesthesias are associated with enhanced dorsal root ganglia (DRG) neuronal outgrowth. Although glycogen synthase kinase-3β (GSK-3β) is a known intracellular regulator neuronal growth, the potential contribution to primary afferent growth responses following SCI are undefined. We hypothesized that SCI triggers inhibition of GSK-3β signaling resulting in enhanced DRG growth responses, and that PI3K mediated activation of GSK-3β can prevent this growth and the development of at-level pain syndromes.
  
  
  RESULTS
  Excitotoxic SCI using intraspinal quisqualic acid (QUIS) resulted in inhibition of GSK-3β in the superficial spinal cord dorsal horn and adjacent DRG. Double immunofluorescent staining showed that GSK-3β(P) was expressed in DRG neurons, especially small nociceptive, CGRP and IB4-positive neurons. Intrathecal administration of a potent PI3-kinase inhibitor (LY294002), a known GSK-3β activator, significantly decreased GSK-3β(P) expression levels in the dorsal horn. QUIS injection resulted in early (3 days) and sustained (14 days) DRG neurite outgrowth of small and subsequently large fibers that was reduced with short term (3 days) administration of LY294002. Furthermore, LY294002 treatment initiated on the date of injury, prevented the development of overgrooming, a spontaneous at-level pain related dysesthesia.
  
  
  CONCLUSIONS
  QUIS induced SCI resulted in inhibition of GSK-3β in primary afferents and enhanced at-level DRG intrinsic growth (neurite elongation and initiation). Early PI3K mediated activation of GSK-3β attenuated QUIS-induced DRG neurite outgrowth and prevented the development of at-level dysesthesias.
authors.affiliation: Department of Physical Therapy, College of Allied Health Sciences, East Carolina University, 600 Moye Blvd., Room 2405E, Greenville, NC, 27834, USA. bareisss@ecu.edu.
authors.forename: Sonja K
authors.initials: SK
authors.lastname: Bareiss
authors.affiliation: Department of Physical Therapy, College of Allied Health Sciences, East Carolina University, 600 Moye Blvd., Room 2405E, Greenville, NC, 27834, USA. e.dugan@med.miami.edu.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Dugan
authors.affiliation: Department of Emergency Medicine, East Carolina University, 600 Moye Blvd., Room 2405E, Greenville, NC, 27834, USA. brewerk@ecu.edu.
authors.forename: Kori L
authors.initials: KL
authors.lastname: Brewer
mesh_terms: D000818:Animals; D002867:Chromones / Q000008:administration & dosage / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005727:Ganglia, Spinal / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D007278:Injections, Spinal; D008297:Male; D009025:Morpholines / Q000008:administration & dosage / Q000494:pharmacology; D016501:Neurites / Q000187:drug effects / Q000473:pathology; D009475:Neurons, Afferent / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology*; D009498:Neurotoxins / Q000633:toxicity*; D059225:Nociception / Q000187:drug effects; D010292:Paresthesia / Q000150:complications* / Q000201:enzymology / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D016318:Quisqualic Acid; D020318:Rats, Long-Evans; D066148:Spinal Cord Dorsal Horn / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D013119:Spinal Cord Injuries / Q000150:complications* / Q000201:enzymology / Q000473:pathology
chemical_list: D002867:Chromones; D009025:Morpholines; D009498:Neurotoxins; D047428:Protein Kinase Inhibitors; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D016318:Quisqualic Acid; D019869:Phosphatidylinositol 3-Kinases; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D038362:Glycogen Synthase Kinase 3