In vivo study of innervation of degenerative intervertebral discs in rabbit anular-injury model

Abstract

To observe degenerative intervertebral disc and to examine innervation of degenerative discs in the rabbit anular-injury model. Two different magnitudes of anular injury at 5 mm depth were performed by 11 blade or 16 gauge needle at the L3-L4 or L5-L6 discs in New Zealand white rabbits (n=48, 2.5-3.0 kg). Disc degeneration was evaluated by radiographic, MRI and histological examination at different time points after surgery. To identify nerve ingrowth into disc, two general markers PGP 9.5 and GAP 43, for nerve fibers were examined by immunohistochemistry. Significant decreases in disc height and signal intensity in magnetic resonance imaging were observed in 11 blade group and 16 G puncture group (P<0.01). 16 G puncture group induced slower and more progressive disc degeneration companed with the stab group and control group. At the 12-week time point, nucleus pulposus tissues were extruded and scar tissues formed outside the disc. In stab discs, nerve ingrowth was scattered on the surface of injury site and in the deeper part of the scar tissues, more than 1 mm from the surface. However, in punctured discs, PGP 9.5 and GAP 43-immunoreative fibers were only observed in the outmost part of the scar tissues and superficial area. More nerve fibers were observed in stab group. Innervation may act as a source of discogenic pain which is associated with intervertebral disc degeneration caused by disc anular injury.