Faculty Collaboration Database

Windup of flexion reflexes in chronic human spinal cord injury: a marker for neuronal plateau potentials? J Neurophysiol 2003 Jan;89(1):416-26

Date

01/11/2003

Pubmed ID

12522190

DOI

10.1152/jn.00979.2001

Scopus ID

2-s2.0-0037250630 (requires institutional sign-in at Scopus site)   94 Citations

Abstract

The physiological basis of flexion spasms in individuals after spinal cord injury (SCI) may involve alterations in the properties of spinal neurons in the flexion reflex pathways. We hypothesize that these changes would be manifested as progressive increases in reflex response with repetitive stimulus application (i.e., "windup") of the flexion reflexes. We investigated the windup of flexion reflex responses in 12 individuals with complete chronic SCI. Flexion reflexes were triggered using trains of electrical stimulation of plantar skin at variable intensities and inter-stimulus intervals. For threshold and suprathreshold stimulation, windup of both peak ankle and hip flexion torques and of integrated tibialis anterior electromyographic activity was observed consistently in all patients at inter-stimulus intervals < or =3 s. For subthreshold stimuli, facilitation of reflexes occurred only at intervals < or =1 s. Similarly, the latency of flexion reflexes decreased significantly at intervals < or =1 s. Patients that were receiving anti-spasticity medications (e.g., baclofen) had surprisingly larger windup of reflex responses than those who did not take such medications, although this difference may be related to differences of spasm frequency between the groups of subjects. The results indicate that the increase in spinal neuronal excitability following a train of electrical stimuli lasts for < or =3 s, similar to previous studies of nociceptive processing. Such long-lasting increases in flexion reflex responses suggest that cellular mechanisms such as plateau potentials in spinal motoneurons, interneurons, or both, may partially mediate spinal cord hyperexcitability in the absence of descending modulatory input.

Author List

Hornby TG, Rymer WZ, Benz EN, 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
Aged
Baclofen
Chronic Disease
Electric Stimulation
Electromyography
Female
Humans
Interneurons
Male
Middle Aged
Motor Neurons
Movement
Muscle Contraction
Muscle Relaxants, Central
Muscle Spasticity
Muscle, Skeletal
Reaction Time
Reflex, Abnormal
Spinal Cord
Spinal Cord Injuries