Sequential Activation of AMPA Receptors and Glial Cells in a Pain Model of Lumbar Spine Disc Herniation

Abstract

Objective To investigate the glial cell and AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor activity after surgery for disc herniation pain model. Methods In total, 83 Sprague-Dawley rats were randomly assigned to the following groups: control (n=16), sham-operated (n=4), rats for pain behavior evaluation (n=3), nucleus pulposus-exposed groups for AMPA receptors (n=30), and glial cell (n=30). The rats were tested for mechanical allodynia; immunohistochemical staining for AMPA receptors (GluAl and GluA2) and glial cells (OX-42 and glial fibrillary acid protein [GFAP]) in the spinal dorsal horn was performed on postoperative days 3, 7, and 14. Results Mechanical withdrawal thresholds decreased after surgery, and this effect was maintained for up to 14 days. Immunohistochemical expression of GluAl and GluA2 in the spinal dorsal horn had increased quantitatively on postoperative days 3 and 7 (p<0.05) to levels similar to that of the controls on postoperative day 14. Moreover, immunohistochemical expression of OX-42 and GFAP showed similar changes to AMPA receptors after surgery. Although the activity of AMPA receptors and glial cells achieved normalcy, the mechanical withdrawal threshold of the hind paw remained decreased 38 days after surgery. Conclusion The rat model of lumbar disc herniation showed increased expression of AMPA receptor and glial cell activity in the spinal dorsal horn 3 and 7 days after surgery, which deceased to control levels at 14 days. The AMPA receptors and glial cell activations showed similar patterns after disc herniation surgery. Keywords AMPA receptors, Intervertebral disc displacement, Spinal cord dorsal horn, Inflammation, Synaptic plasticity