Spinal stenosis: assessment of motor function, VEGF expression and angiogenesis in an experimental model in the rat

Abstract

Reduction of blood flow in compressed nerve roots is considered as one important mechanism of induction of neurogenic intermittent claudication in lumbar spinal canal stenosis. Vascular endothelial growth factor (VEGF) is a potent stimulator of angiogenesis, and is increased in expression in hypoxic conditions. The objective of this study was to examine if cauda equina compression affects motor function and induces expression of VEGF and angiogenesis. The cauda equina was compressed by placing a piece of silicone rubber into the L5 epidural space. Walking duration was examined by rota-rod testing. The compressed parts of the cauda equina and L5 dorsal root ganglion (DRG) were removed at 3, 7, 14, or 28 days after surgery, and processed for immunohistochemistry for VEGF and Factor VIII (marker for vascular endothelial cells). Numbers of VEGF-immunoreactive (IR) cells and vascular density were examined. Walking duration was decreased after induction of cauda equina compression. The number of VEGF-IR cells in the cauda equina and DRG was significantly increased at 3, 14, and 28 days after cauda equina compression, compared with sham-operated rats (P < 0.05). Vascular density in the cauda equina was not increased at any of the time points examined. Cauda equina compression decreased walking duration, and induced VEGF expression in nerve roots and DRG.

Fig. 1

a The surgical procedure for induction of cauda equina compression. A silicon block (length: 4.0 mm, width: 1 mm, thickness: 0.9 mm) was placed into the epidural space under the L5 vertebra through the interlaminar space between L5 and L6. b This is an anatomic photo coinciding with a. Laminectomy was performed for showing a place of silicon block. c This photo shows a cross sectional image of the spinal canal with the silicon block

Fig. 2

Time course of changes in walking time. Results are the mean ± standard deviation of walking duration. There were significant differences between the compression and sham-operated groups at days 1, 3, 7, and 14 after surgery (*P < 0.05)

Fig. 3

Photomicrographs demonstrating VEGF-immunoreactive cells in the cauda equine (a, b) and DRG (c, d) in compression group (a, c) and sham-operated group (b, d) at day 28 after surgery. Schwann-like cells in the cauda equina and DRG neurons exhibited immunoreactivity for VEGF (arrows). Scale bar 50 μm

Fig. 4

Histogram presenting numbers of VEGF-IR cells in the cauda equine (a) and percentages of VEGF-IR neurons in the DRG (b). In the compression group, numbers of VEGF-IR cells in the cauda equina and percentages of VEGF-IR neurons in DRG were significantly increased at days 3, 14, and 28 after surgery compared with the sham-operated group (*P < 0.05). Results are the mean ± standard deviation

Fig. 5

a Photomicrographs demonstrating Factor VIII-immunoreactive blood vessels in the cauda equina of sham-operated rat at day 3 after surgery. Blood vessels are visible after immunostaining for factor VIII. Scale bar 200 μm. b Histogram presenting vascular density in the cauda equina. There were no significant differences between the compression and sham-operated groups at any time point. Results are the mean ± standard deviation of vascular density