Evidence that alterations in presynaptic inhibition contribute to segmental hypo- and hyperexcitability after spinal cord injury in man

Blair Calancie, James G. Broton, K. John Klose, Monique Traad, John Difini, D. Ram Ayyar

Research output: Contribution to journalArticle

168 Scopus citations

Abstract

We examined Hoffmann (H) and tendon (T) reflexes in 3 populations of adult subjects: acute SCI (< 2 weeks post injury), controls, and chronic SCI ( > 1 year post injury). We further investigated the effects of continuous tendon vibration and different stimulus rates on the size of the evoked H reflexes in these subject populations. All reflex amplitudes were expressed as a function of the maximum direct muscle response (M wave), to allow comparison between subjects. Both H and T reflexes were successfully elicited from all subjects examined, including those in 'spinal shock'. Tendon vibration caused a marked attenuation of H reflexes in acute SCI subjects, intermediate attenuation in controls, and relatively little effect in the chronic SCI group. H reflexes showed greatest attenuation for a given stimulus rate in acute SCI subjects compared to controls (intermediate attenuation) or chronic SCI (limited attenuation) subjects. Both rate sensitivity and vibration influence have been linked to presynaptic inhibitory mechanisms. We suggest that spinal cord injury disrupts the supraspinal influence over segmental interneurons mediating presynaptic inhibition, and that the hyporeflexia associated with 'spinal shock' is due in part to a substantial increase in the efficacy of presynaptic inhibition. Conversely, over time the level of presynaptic inhibition of ankle extensor Ia input in SCI subjects declines to levels less than those of control subjects, contributing to the enhancement of spinal reflexes consistent with the clinical state of 'spasticity' seen in chronic SCI.

Original languageEnglish (US)
Pages (from-to)177-186
Number of pages10
JournalElectroencephalography and Clinical Neurophysiology/ Evoked Potentials
Volume89
Issue number3
DOIs
StatePublished - Jun 1993

Keywords

  • H reflex
  • Low frequency depression
  • Presynaptic inhibition
  • Spasticity
  • Spinal cord injury
  • Spinal shock
  • Vibration

ASJC Scopus subject areas

  • Clinical Neurology
  • Neuroscience(all)

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