title: Electrophysiological characterization of spontaneous recovery in deep dorsal horn interneurons after incomplete spinal cord injury.
abstract: In the weeks and months following an incomplete spinal cord injury (SCI) significant spontaneous recovery of function occurs in the absence of any applied therapeutic intervention. The anatomical correlates of this spontaneous plasticity are well characterized, however, the functional changes that occur in spinal cord interneurons after injury are poorly understood. Here we use a T10 hemisection model of SCI in adult mice (9-10 wks old) combined with whole-cell patch clamp electrophysiology and a horizontal spinal cord slice preparation to examine changes in intrinsic membrane and synaptic properties of deep dorsal horn (DDH) interneurons. We made these measurements during short-term (4 wks) and long-term (10 wks) spontaneous recovery after SCI. Several important intrinsic membrane properties are altered in the short-term, but recover to values resembling those of uninjured controls in the longer term. AP discharge patterns are reorganized at both short-term and long-term recovery time points. This is matched by reorganization in the expression of voltage-activated potassium and calcium subthreshold-currents that shape AP discharge. Excitatory synaptic inputs onto DDH interneurons are significantly restructured in long-term SCI mice. Plots of sEPSC peak amplitude vs. rise times suggest considerable dendritic expansion or synaptic reorganization occurs especially during long-term recovery from SCI. Connectivity between descending dorsal column pathways and DDH interneurons is reduced in the short-term, but amplified in long-term recovery. Our results suggest considerable plasticity in both intrinsic and synaptic mechanisms occurs spontaneously in DDH interneurons following SCI and takes a minimum of 10 wks after the initial injury to stabilize.
authors.affiliation: School of Biomedical Sciences & Pharmacy, University of Newcastle, Callaghan, 2308 NSW, Australia.
authors.forename: M M
authors.initials: MM
authors.lastname: Rank
authors.affiliation: School of Biomedical Sciences & Pharmacy, University of Newcastle, Callaghan, 2308 NSW, Australia.
authors.forename: J R
authors.initials: JR
authors.lastname: Flynn
authors.affiliation: Department of Medicine (Royal Melbourne Hospital), The University of Melbourne, 3050 VIC, Australia.
authors.forename: M P
authors.initials: MP
authors.lastname: Galea
authors.affiliation: School of Biomedical Sciences & Pharmacy, University of Newcastle, Callaghan, 2308 NSW, Australia.
authors.forename: R
authors.initials: R
authors.lastname: Callister
authors.affiliation: School of Biomedical Sciences & Pharmacy, University of Newcastle, Callaghan, 2308 NSW, Australia. Electronic address: robert.callister@newcastle.edu.au.
authors.forename: R J
authors.initials: RJ
authors.lastname: Callister
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D055592:Biophysical Phenomena / Q000502:physiology; D001703:Biophysics; D004195:Disease Models, Animal; D004558:Electric Stimulation; D007839:Functional Laterality; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018408:Patch-Clamp Techniques; D020671:Posterior Horn Cells / Q000502:physiology*; D020127:Recovery of Function / Q000502:physiology*; D013119:Spinal Cord Injuries / Q000473:pathology* / Q000503:physiopathology*; D018709:Statistics, Nonparametric; D013997:Time Factors
keywords: Dendritic expansion; Patch clamp; Potassium current; Spinal cord injury; Spontaneous recovery; Synaptic input