Structural properties of spinal nerve roots: Protein composition

The protein compositions of dorsal and ventral spinal nerve roots were determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Protein readily soluble in sodium dodecyl sulfate (SDS) sample buffer made up 8.1% of the wet weight of dorsal and ventral roots. Spinal root protein samples consisted predominantly (60%) of myelin-associated proteins. Other major proteins including those tentatively identified as tubulin, actin, nuclear histones, and others accounted for the remainder of recovered protein. The protein constituents of nerve roots were similar to those of peripheral nerve but differed from those of spinal cord. Nerve roots and peripheral nerve were characterized by fewer major protein bands but greater concentrations of myelin proteins. Collagen which did not readily solubilize in SDS sample buffer was estimated by assaying for hydroxyproline. Nerve roots consisted of approximately 0.4% collagen by weight which was only one-fifth the amount estimated for nerve but six times more than spinal cord. It was apparent that the biomechanical frailty of roots compared with peripheral nerve might be explained by differences in the relative collagen contents of these tissues. The protein constituents of nerve roots after unilateral nerve crush were relatively stable compared with the profound changes seen in ipsilateral nerve and modest changes seen in contralateral uninjured nerve.