Rapid histochemical identification of motor and sensory fascicles: preparation of solutions

Histochemical Identification of Motor Fascicles Using Cholinesterase Staining in Rats Using a Mixed Nerve Model

BACKGROUND

Inappropriate matching of motor and sensory fibers after nerve repair or grafting can lead to nerve recovery failure. Identifying the motor and sensory fascicles enables surgeons to match them accurately and correctly align nerve stumps, which is crucial for neural regeneration. Very few methods have been reported to differentiate between the sensory and motor nerve fascicles, and the replicability of these techniques remains unestablished. In this study, we aimed to assess the accuracy of axonal cholinesterase (CE) histochemical staining in distinguishing motor and sensory nerve fibers.

METHODS

The femoral and sciatic nerves were harvested from rats. The specimens were immediately cut, frozen in isopentane, and cooled with liquid nitrogen. Nerve serial cross-sections were processed for hematoxylin and eosin staining, followed by CE histochemistry. The staining protocol solutions included acetylthiocholine iodide, phosphate buffer, cobalt sulfate hydrate, potassium phosphate monobasic, sulfuric acid, sodium bicarbonate, glutaraldehyde, and ammonium sulfide.

RESULTS

Cross-sections of nerves containing efferent and afferent nerve fibers in segregated fascicles showed that CE activity was confined to motor neurons. A histochemical study revealed that motor fibers with high cholinesterase activity can be differentiated from sensory fibers. The motor branches of the femoral and sciatic nerves showed specific axonal staining, whereas the sensory branch did not show any specific staining.

CONCLUSION

CE histochemical staining is a useful technique for distinguishing between motor and sensory nerve fibers. It can be potentially useful in improving the outcomes of nerve grafts or extremity allotransplantation surgery.

Mixed nerve suture facilitated by enzyme-staining techniques

Identification of motor and sensory fascicles to correctly match the motor and sensory fascicles helps surgeons to correctly align nerve stumps. Motor fibers, with their high cholinesterase activity, can be differentiated from sensory fibers. I developed a new modification that requires less than 1 hour and shows clearer differentiation compared with other histochemical techniques. In my clinical research, proximal stumps can be stained as long as 16 months after injury, however, distal stumps cannot be stained after 5 days. After 5 days, this staining could provide useful proximal information and distal fascicles may be identified by anatomic or topographical knowledge. I think this staining is especially useful in proximal nerve lesions and nerve injuries that require nerve graft within 4 days after injury. Also, this technique is useful in functioning muscle transfer to find motor fascicles and, in a sensate flap, to identify the sensory fascicle.