Faculty Collaboration Database

Temporal facilitation of spastic stretch reflexes following human spinal cord injury. J Physiol 2006 Mar 15;571(Pt 3):593-604

Date

03/17/2006

Pubmed ID

16540600

Pubmed Central ID

PMC1805801

DOI

10.1113/jphysiol.2005.102046

Scopus ID

2-s2.0-33644678110 (requires institutional sign-in at Scopus site)   42 Citations

Abstract

Recent evidence suggests that alterations in ionic conductances in spinal motoneurones, specifically the manifestation of persistent inward currents, may be partly responsible for the appearance of hyperexcitable reflexes following spinal cord injury (SCI). We hypothesized that such alterations would manifest as temporal facilitation of stretch reflexes in human SCI. Controlled, triangular wave, ankle joint rotations applied at variable velocities (30-120 deg s(-1)) and intervals between stretches (0.25-5.0 s) were performed on 14 SCI subjects with velocity-dependent, hyperexcitable plantarflexors. Repeated stretch elicited significant increases in plantarflexion torques and electromyographic (EMG) activity from the soleus (SOL) and medial gastrocnemius (MG). At higher velocities (> or = 90 deg s(-1)), reflex torques declined initially, but subsequently increased to levels exceeding the initial response, while mean EMG responses increased throughout the joint perturbations. At lower velocities (< or = 60 deg s(-1)), both joint torques and EMGs increased gradually. Throughout a range of angular velocities, reflex responses increased significantly only at intervals < or = 1 s between stretches and following at least four rotations. Ramp-and-hold perturbations used to elicit tonic stretch reflexes revealed significantly prolonged EMG responses following one or two triangular stretches, as compared to single ramp-and-hold excursions. Post hoc analyses revealed reduced reflex facilitation in subjects using baclofen to control spastic behaviours. Evidence of stretch reflex facilitation post-SCI may reflect changes in underlying neuronal properties and provide insight into the mechanisms underlying spastic reflexes.

Author List

Hornby TG, Kahn JH, Wu M, Schmit BD

Author

Brian Schmit PhD Professor in the Biomedical Engineering department at Marquette University

MESH terms used to index this publication - Major topics in bold

Adult
Ankle Joint
Baclofen
Electromyography
Female
Humans
Male
Middle Aged
Motor Neurons
Muscle Contraction
Muscle Relaxants, Central
Muscle, Skeletal
Reflex, Abnormal
Reflex, Stretch
Spasm
Spinal Cord Injuries
Time Factors
Torque