Vascularization of the dorsal root ganglia and peripheral nerve of the mouse: implications for chemical-induced peripheral sensory neuropathies

Abstract

Although a variety of industrial chemicals, as well as several chemotherapeutic agents used to treat cancer or HIV, preferentially induce a peripheral sensory neuropathy what remains unclear is why these agents induce a sensory vs. a motor or mixed neuropathy. Previous studies have shown that the endothelial cells that vascularize the dorsal root ganglion (DRG), which houses the primary afferent sensory neurons, are unique in that they have large fenestrations and are permeable to a variety of low and high molecular weight agents. In the present report we used whole-mount preparations, immunohistochemistry, and confocal laser scanning microscopy to show that the cell body-rich area of the L4 mouse DRG has a 7 fold higher density of CD31+ capillaries than cell fiber rich area of the DRG or the distal or proximal aspect of the sciatic nerve. This dense vascularization, coupled with the high permeability of these capillaries, may synergistically contribute, and in part explain, why many potentially neurotoxic agents preferentially accumulate and injure cells within the DRG. Currently, cancer survivors and HIV patients constitute the largest and most rapidly expanding groups that have chemically induced peripheral sensory neuropathy. Understanding the unique aspects of the vascularization of the DRG and closing the endothelial fenestrations of the rich vascular bed of capillaries that vascularize the DRG before intravenous administration of anti-neoplastic or anti-HIV therapies, may offer a mechanism based approach to attenuate these chemically induced peripheral neuropathies in these patients.

Figure 1

Whole mount preparation showing the vascularization of the cell body rich area of the dorsal root ganglia (DRG) vs. the dorsal and ventral roots and sciatic nerve at L4 in the C3H mouse. Bright-field photomicrograph of a whole-mount L4 DRG preparation for anatomical reference. Dashed line demarks the cell body-rich area from the sciatic nerve and dorsal and ventral spinal roots (A). Representative confocal micrograph of a mouse L4 DRG labeled with the endothelial cell marker CD31 showing the marked difference in the density of the vascular supply within the sensory ganglia as compared to the corresponding spinal nerve and dorsal root (B). This dense vascularization of the DRG along with the large fenestrations of the blood vessels in the DRG may partially explain why certain neurotoxics preferential accumulate in the DRG and produce a primarily sensory vs. motor neuropathy. The confocal image in (B) was assembled from 280 optical sections acquired at 0.5 μm z-plane intervals so that the total z stack is 140 μm-thick. Scale bar = 100 μm.

Figure 2

The density of CD31+ vessels is site dependent within the mouse lumbar dorsal root ganglia (DRG). Representative 3D reconstructed confocal images of L4 DRG whole mount preparation from thy1-YFP transgenic mice where the cell body and axons of sensory neurons constitutively express yellow fluorescent protein (YFP, pseudocolored violet). In contrast, the endothelial cells were immunohistochemically labeled with a marker of platelet endothelial cell adhesion molecule, CD31+ (green) (A, B). Note that a dense vascular plexus surrounds sensory neuron cell bodies within cell body-rich areas (C), whereas the nerve fiber-rich areas have a lower density of CD31+ vascular labeling (D). The confocal image in A-D were acquired at 0.5 μm z-plane intervals and the total z-plane for (A) 90 μm, (B) 60 μm and (C&D) 15 μm. Scale bar A-D = 50 μm.

Figure 3

CD31⁺ blood vessel density is significantly higher in cell body-rich areas (CBRA) as compared to nerve fiber-rich areas (NFRA) of the L4 dorsal root ganglia (DRG) and distal and proximal sciatic nerve of the C3H mouse. Regional differences in blood vessel density were determined by quantifying the CD31⁺ blood vessels/mm² in 15 μm cut sections of the L4 DRG and attached nerve roots. Each bar of the histograms represents the mean +/- SEM of at least 4 mice and * indicates a difference of p < 0.05 vs CBRA of the L4 DRG.