AUTHOR=Barbe Mary F. , Chen Frank Liu , Loomis Regina H. , Harris Michele Y. , Kim Brandon M. , Xie Kevin , Hilliard Brendan A. , McGonagle Elizabeth R. , Bailey Taylor D. , Gares Ryan P. , Van Der Bas Megan , Kalicharan Betsy A. , Holt-Bright Lewis , Stone Laura S. , Hodges Paul W. , Klyne David M. TITLE=Characterization of pain-related behaviors in a rat model of acute-to-chronic low back pain: single vs. multi-level disc injury JOURNAL=Frontiers in Pain Research VOLUME=5 YEAR=2024 URL=https://www.frontiersin.org/journals/pain-research/articles/10.3389/fpain.2024.1394017 DOI=10.3389/fpain.2024.1394017 ISSN=2673-561X ABSTRACT=Introduction

Low back pain is the most common type of chronic pain. We examined pain-related behaviors across 18 weeks in rats that received injury to one or two lumbar intervertebral discs (IVD) to determine if multi-level disc injuries enhance/prolong pain.

Methods

Twenty-three Sprague-Dawley adult female rats were used: 8 received disc puncture (DP) of one lumbar IVD (L5/6, DP-1); 8 received DP of two lumbar IVDs (L4/5 & L5/6, DP-2); 8 underwent sham surgery.

Results

DP-2 rats showed local (low back) sensitivity to pressure at 6- and 12-weeks post-injury, and remote sensitivity to pressure (upper thighs) at 12- and 18-weeks and touch (hind paws) at 6, 12 and 18-weeks. DP-1 rats showed local and remote pressure sensitivity at 12-weeks only (and no tactile sensitivity), relative to Sham DP rats. Both DP groups showed reduced distance traveled during gait testing over multiple weeks, compared to pre-injury; only DP-2 rats showed reduced distance relative to Sham DP rats at 12-weeks. DP-2 rats displayed reduced positive interactions with a novel adult female rat at 3-weeks and hesitation and freezing during gait assays from 6-weeks onwards. At study end (18-weeks), radiological and histological analyses revealed reduced disc height and degeneration of punctured IVDs. Serum BDNF and TNFα levels were higher at 18-weeks in DP-2 rats, relative to Sham DP rats, and levels correlated positively with remote sensitivity in hind paws (tactile) and thighs (pressure).

Discussion

Thus, multi-level disc injuries resulted in earlier, prolonged and greater discomfort locally and remotely, than single-level disc injury. BDNF and TNFα may have contributing roles.