Regeneration of sciatic nerve in frogs maintained at 15 degrees C: failure to sustain regeneration after initiation.
Peripheral nerve regeneration proceeds through a series of phases which include axonal sprouting, elongation, and maturation. Each phase requires interaction between intrinsic properties of the injured neuron and nonneural elements in the environment into which the nerve grows. It has been difficult, however, to separate processes which depend on the induction of a cell body response from those which may depend on local factors at the site of injury. Recently, we found that frog peripheral nerves, in animals housed at 15 degrees C, were able to initiate regeneration in the absence of an apparent cell body response. Subsequently, we found that these nerves did not continue to regenerate normally. I investigated the ultrastructure of regenerating nerves from frogs kept at 15 degrees C for 92 days after a freeze-lesion. Injured sciatic nerves showed extensive axonal sprouting at the lesion site but little continued growth distal to the injury, indicating an impairment in elongation and maturation. Nonneural cells in the local environment showed extensive distributions of rough endoplasmic reticulum and free ribosomes near the regenerative sprouts but the type and quantity of protein actually being synthesized was not determined. The basis for the suppression of axonal growth remains unknown but in the absence of an apparent cell body response it appears probable that a necessary cell body contribution to regeneration was also absent. That contribution could provide direct support to axonal growth or could trigger periaxonal support of regeneration. This experimental preparation offers a means of investigating those alternatives and the opportunity to determine the origin of the various processes responsible for nerve regeneration.
D000818:Animals; D001369:Axons / Q000648:ultrastructure; D003080:Cold Temperature; D009416:Nerve Regeneration; D011894:Rana pipiens; D012584:Sciatic Nerve / Q000502:physiology* / Q000648:ultrastructure