Histopathology
Mice were anesthetized with ethyl ether. Whole-body perfusion by 2% paraformaldehyde-glutaraldehyde solution followed by heparin-included saline was performed. Sciatic nerves, trigeminal nerves, brain and spinal cord were removed and fixed in 10% neutral-buffered formalin. The spinal cord and other nerve blocks were washed and postfixed with 2% osmium tetroxide, and were dehydrated in ethanol and equilibrated in Epon. Epon embedded semithin sections were stained with toluidine blue and were subjected to light microscopic examination. For electron microscopic analysis, thin sections were cut using an ultramicrotome, stained with 1.5% uranylacetate in 50% ethanol and 0.8% lead citrate, and analysed using electron microscope. All procedures were conducted according to the Eisai Animal Care Committee's guidelines.