Effects of Axotomy on the Cholinesterase and Carbonic Anhydrase Activities of Axons in the Proximal and Distal Stumps of Rabbit Sciatic Nerves

Abstract

The temporal changes in transected sciatic nerves of rabbits were studied using recently developed histochemical techniques for discriminating between sensory and motor axons. A segment of the nerve was removed to inhibit spontaneous regeneration across the gap. Staining characteristics of the proximal and distal nerve stumps were studied at 1, 2, 3, 4, 9, and 35 days following axotomy and compared with control sciatic nerves. In the control and test nerves, subpopulations of myelinated sensory axons were identified histochemically by carbonic anhydrase (CA) staining, and a subset of alpha motor axons were visualized by cholinesterase (CE) staining. Axon staining patterns were reciprocal; i.e., sensory axons were CA-positive and CE-negative, whereas motor axons were CE-positive and CA-negative. Histochemical activities persisted at day 35 after axotomy in the proximal stump and until day 9 after axotomy in the distal stump. This implies that these techniques may aid in both immediate and delayed primary nerve repair. With time, there is buildup of scar tissue adding to the proximal and distal stumps. Therefore, sections for demonstrating sensory and motor axons must be taken progressively further back from the nerve stump ends. Histochemical axon typing indicated that sensory axons regenerated earlier and to a greater degree than motor axons in the developing neuroma. Use of both the carbonic anhydrase and cholinesterase staining methods is more accurate than either technique alone as an adjunct for examining normal and injured peripheral nerves.