Trochlear nerve regeneration in Xenopus laevis larvae.
The trochlear nerve of Xenopus laevis larvae was sectioned in the orbit, and the nerve distal to the section was removed, so that it could not serve to guide the return of the regenerating nerve to the superior oblique muscle (SOM). In a second series, in addition to removing the distal nerve segment, the SOM was removed or damaged. The regeneration pattern of the trochlear nerve fibers was recorded in situ at 1 to 5-day intervals with the aid of methylene blue staining. The early growth or regenerating fibers was multidirectional; only some fibers encountered the SOM by day 6 or 7; others reached nerves, inappropriate muscle, and other tissues. Ultimately, the fibers that reached the SOM persisted and were reinforced, while those that reached other locations were withdrawn. By 20 days or so, the regenerated trochlear nerve usually had an appearance that was close to that of an uncut nerve. In the second series, in which the SOM was removed or damaged, the multidirectional character of the growth persisted through 20 days after section. these data suggest that: 1) Trochlear nerve regeneration is not guided by cues that closely control fiber growth along a direct path to the SOM, and 2) The SOM acts as a trap for regenerating trochlear nerve fibers, promoting the maintenance and the fasciculation of the trochlear nerve fibers that reach it, and the degeneration of the fibers that do not.
D000818:Animals; D007814:Larva / Q000502:physiology; D009416:Nerve Regeneration; D009801:Oculomotor Muscles / Q000294:innervation*; D013997:Time Factors; D014321:Trochlear Nerve / Q000033:anatomy & histology / Q000502:physiology; D014981:Xenopus / Q000502:physiology*