Goldfish retina and tectum influence each other's growth activity during regrowth of the retinotectal projection

Variations in retinal and tectal growth activity, during regrowth of the goldfish retinotectal projection, were monitored by measuring the rates of incorporation of [14C]leucine into soluble protein and tubulin-enriched fractions at different times after crushing the optic nerves. Other experiments tested for growth-modulating interactions between tectum and retina. Here we studied how the absence of one of these structures (i.e. tectal ablation or eye removal) affected the profile of biosynthetic activity in the other. Experiments were also conducted on groups of fish in which the tectum was reinnervated by a half-retina (either half-nasal (1/2 N) or half-temporal (1/2 T) retina). This was done to ascertain if growth interactions between retina and tectum display any position-dependent differences that may be relevant to retinotopic ordering during regeneration. Our studies have revealed that: the retina and tectum of 1/2 T and 1/2 N groups differ in their growth responses during regeneration of the visual pathway: the tectum may exert a stimulatory and at other times an inhibitory influence on retinal protein synthesis; and retina and tectum display a bimodal profile of biosynthetic activity during regeneration that coincides with two stages of increased cell division (primarily glia) which other workers have found occurs in the tectum and tract during regeneration of the retinotectal projection. Indeed it seems there may be a link between this glial proliferation and the neurotrophic and guiding influences which tectum and retina exert upon one another during regeneration.