Adaptation of tibial nerve myelinated fibre parameters to reduced limb length caused by irradiation.

Irradiation of a rat hind limb at 15 days of age caused marked shortening of the limb, with a consequent reduction in nerve length. The tibial nerves of the irradiated limbs were examined qualitatively and quantitatively, and compared with the unirradiated nerve. There was no evidence of fibre degeneration and only very occasional myelin abnormalities. Myelinated fibre numbers were very slightly reduced, possibly due to irradiation effects on small myelinated fibres. Internodal lengths were reduced in proportion to limb length. Mean axon diameters were slightly increased, and myelin sheath thickness reduced. This experimental model provides a new method of altering nerve fibre parameters without surgical intervention.