Figure 3. Morphologic changes in transverse sections of sciatic nerve with and without the injection of 0.1 ml of 37 mM N-butyl tetracaine. Histologic cross sections of rat peripheral nerve were stained with hematoxylin and eosin. (A) Normal rat peripheral nerve contralateral to the site of injection 21 days after injection. The axoplasm forms a central eosinophilic region within each axonal fiber, with either a clear or a halo with radiating spokes corresponding to the myelin sheath. Large-caliber myelinated fibers are closely apposed to each other (magnification, x720). (B) Acute stages of axonal degeneration show vacuolation of most myelinated fibers. The increase in the number of nuclei is due to the proliferation of Schwann cells and an influx of macrophages (magnification, x720). (C) Normal rat peripheral nerve contralateral to the site of injection 35 days after injection (magnification, x720). (D) At 35 days, large vacuolated fibers (which represent acute stages of axonal degeneration) are less prominent in the sciatic nerve from the site of injection, although an increase in cellularity is evident. Pale eosinophilic regions within the endoneurial space without discernible axonal profiles correspond to areas of axonal loss and fibrosis (magnification, x720).