Microsurgical transection of small nerve fibre bundles in vitro. Effects on axons, growth cones and glial cells.

Fibres growing from neurons of explanted dorsal root ganglia from 10 day chick embryos were transected and subsequently observed by light and electron microscopy after periods of a few to fifty minutes. Changes immediately proximal and distal to the cut together with alterations further away from the site of injury on both sides of the cut were recorded. Observations were also made on the growth cones of damaged axons and on changes in associated glial cells. Reactive and degenerative changes including the rotation, retraction and swelling of cutaxons occurred rapidly. Electron microscopy revealed tracts of filamentous material close to the sealed-off ends of axons, swollen organelles such as mitochondria, and lamellar bodies of varying dimensions. Proximal to the injury and closer to the explant, damaged and degenerating axons mingled with normal processes. Many contained only a fine granular material, others clumps of organelles, particularly mitochondria. Distal to the cut, microspikes were lost from some growth cones. The dense granular material filling microspikes and growth cones remained unchanged. Clumps of large clear vesicles, lamellar bodies and swollen degenerating mitochondria were present, not only within growth cones, but also in all parts of the axon distal to the cut. Glial cells associated with transected axons soon developed an electron dense cytoplasm containing swollen organelles. Large numbers of vesicles filled with a particulate substance were also found. The possible significance of the changes observed after transection are considered and discussed.