“Extra” optic fibers exclude normal fibers from tectal regions in goldfish

Abstract

A small group of selected optic fibers were surgically deflected from one tectum into the other, thus creating a novel additional projection originating from a small area of ipsilateral retina. The normal fibers to this "recipient" tectum were also severed so that both the deflected and the normal fibers regrew into this tectum at about the same time. The reinnervation pattern was analyzed by autoradiography and electrophysiologic mapping. Both techniques showed that the deflected fibers and the "normal" fibers failed to intermix. The deflected fibers typically formed several well-defined patches of innervation in roughly the appropriate region of denervated recipient tectum. The normal fibers filled in the remaining uninnervated tectal areas and were completely or nearly completely exculded from the patches occupied by the deflected fibers. This segregation was often quite sharp having an apparent average overlap less than 25-50 micron. The electrophysiology indicated that the projections of both deflected and normal fibers were retinotopically organized but that the mapping by the normal fibers was compressed. This compression, an apparent consequence of being squeezed onto a smaller than normal region of tectum, was similar to that previously observed following ablations of part of the tectum. The negligible surgical damage in the present experiment, however, excludes the kind of cytochemical reorganization previously suggested to produce compression. The findings also provide evidence for a competitive type of interaction between optic fibers.

Right and left eye bands in frogs with unilateral tectal ablations.

“…Our findings are consistent with a number of anatomical investigations that mention similar but apparently more variably sized bands or patches of ipsilateral eye terminals in single-tectum Xenopus, goldfish, and rats (22)(23)(24)(25)(26)(27)(28)(29). In goldfish, segregation of both normal and anomalous projections has been demonstrated after deflections of optic tract fibers onto ipsilateral tecta that were simultaneously deprived of existing retinal input by optic nerve crush (23).…”

“…In goldfish, segregation of both normal and anomalous projections has been demonstrated after deflections of optic tract fibers onto ipsilateral tecta that were simultaneously deprived of existing retinal input by optic nerve crush (23).…”

Resistance of a crayfish sensory interneurone to hyperinnervation by acceptable afferents.

“…The symmetry is also a result of some independent interest, because to our knowledge the degree to which bilaterally homologous neurones are interchangable during development or regeneration has seldom been studied. Most of the work we know ofon optic tectum (Schneider, 1973;Sharma, 1973;Levine & Jacobson, 1975;Schmidt, 1977;Meyer, 1979 (for a contradictory result see Cronly-Dillon & Glaizner 1974), on crayfish tonic flexor muscles (Hunt & Velez, 1979), and on cereal inputs to the last abdominal ganglion of crickets (Palka & Schubiger, 1975) -is consistent with our observations in finding a lack of intrinsic side specificity. It should, however, be admitted that regeneration, even under conditions of competition, may not be the most sensitive possible test of selective affinity.…”

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

“…Similarly, when half of retina is removed and the nerve crushed, regenerating fibers from the remaining half of retina can expanded across the entire tectum (36). Since the general result is that all fibers become accommodated and all tectum becomes innervated, it has been suggested that fibers compete for tectal space (18,26,39,42).…”

“…There are reasons to believe that the regulation of axonal growth is more complicated than a simple response to local cues. One reason for thinking this is the plasticity of the mapping (13,26,36,39,42,44). When half of tectum is removed, fibers will form a compressed retinotopic projection onto the remaining half of tectum.…”