Staining of regenerated optic arbors in goldfish tectum: Progressive changes in immature arbors and a comparison of mature regenerated arbors with normal arbors

Abstract

Individual optic arbors, normal and regenerated, were stained via anterograde transport of HRP and viewed in tectal whole mounts. Camera lucida drawings were made of 119 normal optic arbors and of 242 regenerated arbors from fish 2 weeks to 14 months postcrush. These arbors were analyzed for axonal trajectory, spatial extent in the horizontal plane, degree of branching, number of branch endings, average depth, and degree of stratification. Normal optic arbors ranged in size from roughly 100 to 400 microns across in a continuous distribution, had an average of 20 branch endings with average of fifth-order branching, and were highly stratified into one of three planes within the major optic lamina (SO-SFGS). Small arbors arising from fine-caliber axons terminated in the most superficial plane of SO-SFGS; large arbors from coarse axons terminated in the superficial and middle planes; and medium arbors from medium-caliber axons terminated in the middle and deep planes of SO-SFGS, as well as deeper in the central gray and deep white layers. Arbors from central tectum tended to be much more tightly stratified than those in the periphery. No other differences between central and peripheral arbors were noted. Mature regenerated arbors (five months or more postcrush) were normal in their number of branch endings, order of branching, and depth of termination. Their branches covered a wider area of tectum, partially because of their early branching and abnormal trajectories of branches. Axonal trajectories were often abnormal with U-turns and tortuos paths. Fine-, medium-, and coarse-caliber axons were again present and gave rise to small, medium, and large arbors at roughly the same depths as in the normals. There was frequently a lack of stratification in the medium and large arbors, which spanned much greater depths than normal. Overall, however, regenerates reestablished nearly normal morphology except for axonal trajectory and stratification. Early in regeneration, the arbors went through a series of changes. At 2 weeks postcrush, regenerated axons had grown branches over a wider-than-normal extent of tectum, though they were sparsely branched and often tipped with growth cones. At 3 weeks, the branches were more numerous and covered a still wider extent (average of five times normal), many covering more than half the tectal length or width. At 4-5 weeks smaller arbors predominated, although a few enlarged arbors were present for up to 8 weeks. Additional small changes occurred beyond 8 weeks as the arbors became progressively more normal in appearance.(ABSTRACT TRUNCATED AT 400 WORDS)

Topographic Restriction of TAG-1 Expression in the Developing Retinotectal Pathway and Target Dependent Reexpression during Axon Regeneration

“…In rodents, TAG-1 expression disappears from RGCs within 2 days after optic nerve lesion and is not reexpressed, even in the axons that regenerate in the presence of a sciatic nerve transplant (Jung et al, 1997). During regeneration in adult fish, axons neither reform age-related bundles-which correlates with the fact that all axons reexpress the IgSF CAM E587 antigen-nor do they segregate according to their origin from retinal sectors (Stuermer and Easter, 1984a;Stuermer, 1988b,c;Schmidt et al, 1988;Bastmeyer et al, 1990). If TAG-1 promotes recognition and fasciculation of nasal RGC axons during development, its delayed and target-dependent reexpression during regeneration could account for the disorder among the axons.…”

“…It is known that many regenerating axons take abnormal routes and branch widely in the tectum before they reach and restrict their arbors to retinotopically appropriate sites (Stuermer, 1988b,c;Schmidt et al, 1988). It is conceivable that temporal RGCs erring into the caudal tectum are the ones that reexpress TAG-1 implying that contact with the caudal tectum is the relevant cue for TAG-1 upregulation.…”

“…The first regenerating axons arrive in the rostral tectum between 10 and 12 days after lesion and establish synaptic connections (often in retinotopically incorrect regions), with tectal neurons soon after their arrival (Stuermer and Easter, 1984a). The tectum is invaded by regenerating axons at around 4 weeks after lesion, but it takes several weeks for the retinotopic projection to establish its near-normal order (Stuermer, 1988b,c;Schmidt et al, 1988).…”

Growth behavior of retinotectal axons in live zebrafish embryos under TTX‐induced neural impulse blockade

“…Scale bar = 20 ~m. 1984; Schmidt et al, 1988) as weIl as in embryos (Stuermer and Raymond, 1989;Kaethner and Stuermer, 1992;Schmidt and Buzzard, 1993) .. (S.D., ±11.5 ,um) and 29.9,um (S.o., ±I7.9 ,um), respectively. The areas oftectum that they occupied were 0.9%-5.5% of tectum for TIX and 1.1 %-6.0% for normal arbors according to the first method (that is, encircling the tips ofbranches), and 0.5%-1.3% for TTX (Table 3) and 0.7%-1.4% for normal arbors according to the second method (that is, adding squares occupied by branches).…”

Growth dynamics and morphology of regenerating optic fibers in tectum are altered by injury conditions: An in vivo imaging study in goldfish

“…During the second month, this difference disappeared. Nerve crushed fibers began to form branches and elaborated a terminal arbor by 60 days (8,38). This corresponds to the time when good retinotopic order is reestablished (28,34).…”