Spinal Cord Stimulation Reduces Mechanical Hyperalgesia and Glial Cell Activation in Animals with Neuropathic Pain

Sato, Karina L. PT, PhD*; Johanek, Lisa M. PhD; Sanada, Luciana S. PT*; Sluka, Kathleen A. PhD, PT*

Anesthesia & Analgesia:
doi: 10.1213/ANE.0000000000000047
Pain and Analgesic Mechanisms: Research Report
Abstract

BACKGROUND: Spinal cord stimulation (SCS) is commonly used for neuropathic pain; the optimal variables and mechanisms of action are unclear. We tested whether modulation of SCS variables improved analgesia in animals with neuropathic pain by comparing 6-hour vs 30-minute duration and 50%, 75%, or 90% motor threshold (MT) intensity (amplitude). Furthermore, we examined whether maximally effective SCS reduced glial activation in the spinal cord in neuropathic animals.

METHODS: Sprague-Dawley rats received the spared nerve injury model and were implanted with an epidural SCS lead. Animals were tested for mechanical withdrawal threshold of the paw before and 2 weeks after spared nerve injury, before and after SCS daily for 4 days, and 1, 4, and 9 days after SCS. Spinal cords were examined for the effects of SCS on glial cell activation.

RESULTS: The mechanical withdrawal threshold decreased, and glial immunoreactivity increased 2 weeks after spared nerve injury. For duration, 6-hour SCS significantly increased the mechanical withdrawal threshold when compared with 30-minute SCS or sham SCS; 30-minute SCS was greater than sham SCS. For intensity (amplitude), 90% MT SCS significantly increased the withdrawal threshold when compared with 75% MT SCS, 50% MT SCS, and sham SCS. Both 4 and 60 Hz SCS decreased glial activation (GFAP, MCP-1, and OX-42) in the spinal cord dorsal horn when compared with sham.

CONCLUSIONS: Six-hour duration SCS with 90% MT showed the largest increase in mechanical withdrawal threshold, suggesting that the variables of stimulation are important for clinical effectiveness. One potential mechanism for SCS may be to reduce glial activation at the level of the spinal cord.

In Brief

Published ahead of print December 19, 2013

Author Information

From the *Department of Physical Therapy, University of Iowa, Iowa City, Iowa; and Medtronic, Minneapolis, Minnesota.

Accepted for publication November 11, 2013.

Published ahead of print December 19, 2013

Funding: Funded by Medtronic, Inc. and NIH AR052316 (KAS).

Conflict of Interest: See Disclosures at the end of the article.

Reprints will not be available from the authors.

Address correspondence to Kathleen A. Sluka, PhD, PT, Department of Physical Therapy, University of Iowa Carver College of Medicine, 500 Newton Rd., 1–248 Medical Education Building, Iowa City, IA 52242. Address e-mail to kathleen-sluka@uiowa.edu.

© 2014 International Anesthesia Research Society