title: Depression of involuntary activity in muscles paralyzed by spinal cord injury.
abstract: Involuntary muscle contractions are common after spinal cord injury (SCI). Increased sensitivity to Ia muscle afferent input may contribute to the development of these spasms. Since tendon vibration results in a period of postactivation depression of the Ia synapse, we sought to determine whether Achilles tendon vibration (80 HZ for 2 s) altered involuntary contractions evoked by superficial peroneal nerve (SPN) stimulation (5 pulses at 300 HZ) in paralyzed leg muscles of subjects with chronic (>1 year) SCI. Responses to SPN stimulation that were conditioned by vibration were reduced in 66% of trials (by 33+/-12% in tibialis anterior and 40+/-16% in soleus). These reductions in electromyographic activity are unlikely to be mediated by changes at the Ia synapse or motoneuron because vibration did not alter the magnitude of the soleus H reflex. The electromyographic reductions may involve long-lasting neuromodulatory effects on spinal inhibitory interneurons or synapses involved in the flexor reflex pathway. Vibration-evoked depression of electromyographic activity may be clinically useful in controlling involuntary muscle contractions after SCI.
authors.affiliation: The Miami Project to Cure Paralysis and Department of Neurological Surgery, University of Miami, 1095 NW 14th Terrace, R-48, Miami, Florida 33136, USA.
authors.forename: Jane E
authors.initials: JE
authors.lastname: Butler
authors.forename: Sharlene
authors.initials: S
authors.lastname: Godfrey
authors.forename: Christine K
authors.initials: CK
authors.lastname: Thomas
mesh_terms: D000328:Adult; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology / Q000528:radiation effects; D005260:Female; D006181:H-Reflex / Q000528:radiation effects; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology* / Q000528:radiation effects; D018482:Muscle, Skeletal / Q000503:physiopathology* / Q000528:radiation effects; D009135:Muscular Diseases / Q000209:etiology*; D009433:Neural Inhibition; D010243:Paralysis / Q000209:etiology*; D011930:Reaction Time / Q000528:radiation effects; D013119:Spinal Cord Injuries / Q000150:complications* / Q000503:physiopathology