Spinal cord injury causes plasticity in a subpopulation of lamina I GABAergic interneurons.
Dysfunction of the spinal GABAergic system has been implicated in pain syndromes following spinal cord injury (SCI). Since lamina I is involved in nociceptive and thermal signaling, we characterized the effects of chronic SCI on the cellular properties of its GABAergic neurons fluorescently identified in spinal slices from GAD67-GFP transgenic mice. Whole cell recordings were obtained from the lumbar cord of 13- to 17-day-old mice, including those having had a thoracic segment (T8-11) removed 6-9 days prior to experiments. Following chronic SCI, the distribution, incidence, and firing classes of GFP+ cells remained similar to controls, and there were minimal changes in membrane properties in cells that responded to current injection with a single spike. In contrast, cells displaying tonic/initial burst firing had more depolarized membrane potentials, increased steady-state outward currents, and increased spike heights. Moreover, higher firing frequencies and spontaneous plateau potentials were much more prevalent after chronic SCI, and these changes occurred predominantly in cells displaying a tonic firing pattern. Persistent inward currents (PICs) were observed in a similar fraction of cells from spinal transects and may have contributed to these plateaus. Persistent Na+ and L-type Ca2+ channels likely contributed to the currents as both were identified pharmacologically. In conclusion, chronic SCI induces a plastic response in a subpopulation of lamina I GABAergic interneurons. Alterations are directed toward amplifying neuronal responsiveness. How these changes alter spinal sensory integration and whether they contribute to sensory dysfunction remains to be elucidated.
Dougherty
Kimberly J
KJ
Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Hochman
Shawn
S
D000818:Animals; D000831:Animals, Newborn; D002104:Cadmium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004195:Disease Models, Animal; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D066298:In Vitro Techniques; D007395:Interneurons / Q000145:classification / Q000502:physiology*; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D051379:Mice; D008822:Mice, Transgenic; D009473:Neuronal Plasticity / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods; D026902:Potassium Channel Blockers / Q000494:pharmacology; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013119:Spinal Cord Injuries / Q000473:pathology* / Q000503:physiopathology*; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002121:Calcium Channel Blockers; D026902:Potassium Channel Blockers; D026941:Sodium Channel Blockers; D002104:Cadmium; D049452:Green Fluorescent Proteins; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1