PURPOSE:
Cytokine expression and neuroglial activation in compressed or inflamed dorsal root ganglion (DRG) are the underlying causes of painful radiculopathy. Epineural sheath demonstrated neuroregenerative potential in peripheral nerve repair. The goal of this study is to evaluate the role of the epineural sheath in DRG inflammation. We hypothesize that epineural sheath can provide a unique environment for regeneration after nerve root injury.
METHODS:
A lumbar hemilaminectomy exposing the left L4 DRG and nerve root was performed in 24 rats. Three 3mm pieces of 4-0 chromic-gut suture were placed on the exposed DRG. The right side of the spine was left undisturbed. Animals were re-operated 3 days after initial surgery. Two procedures were investigated: Group I: chromic-gut was removed; Group II: chromic-gut was removed, DRG was wrapped, without compression, with epineural sheath harvested from sciatic nerve of the donor rat. Animals were then closed in a standard fashion and evaluated for presence of gait disturbances 1, 2, 3, 7, 14, 28 days after the second surgery. Functional outcome was assessed by somatosensory evoked potentials (SSEP). Bilateral DRG and epineural sheath were harvested and immunostained for VEGF and GFAP expression.
RESULTS:
Minor gait disturbances were observed, but resolved by 14 days. In Group II SSEP recordings showed shorter P1 and N2 latencies bilaterally compared to Group I, N2 amplitudes were higher in Group I. The highest VEGF expression in the epineural sheath was observed at day 7. In Group I operated side 48% of satellite cells (SC) were GFAP positive at day 1, 80% at day 2, decreasing to 25% at 14 days and increasing again to 38% at 28 days. Group II treated side showed initial decrease in number of GFAP positive SC (from 59% at day 1 to 32% at day 2) followed by maintained number of GFAP positive SC at 45%, 41%, 47%, 40% at day 3, 7, 14, 28 respectively. Number of GFAP positive SC of the contralateral DRG in both groups decreased over time from day 1 (65% in Group I, 53% in Group II) till day 28 (12% in Group I and 10% in Group II). From day 1 to day 2 number of VEGF positive neurons in Group II decreased from 100% to 46%, 95% at day 7 and 23% at day 28. In Group I, 78%, 97%, 95%, 60% of neurons expressed VEGF at day 1, 2, 7 and 28 respectively. In Group I and II contralateral side 100% of neurons expressed VEGF at day 1, 2, 3, 7, 60% at day 14, while at day 28, 95% of neurons expressed VEGF in Group I compared to 60% in Group II.
CONCLUSION:
Epineural sheath patch demonstrated neuroprotective properties in the DRG inflammation model. This was confirmed by improvement in functional recovery by SSEP testing and correlated with decreased expression of GFAP in SC in early phase of inflammation and by heightened expression of VEGF in epineural sheath 7 days after the inflammatory insult.