The response of optic tract glia during regeneration of the goldfish visual system. II. Tectal factors stimulate optic tract glia

After transection, retinal ganglion cell axons of the goldfish will regenerate by growing into a primary target tissue, the optic tectum. To determine what role the target tissue may play in regulating glial cell growth, we measured biosynthetic activity of optic tract glia following excision of the optic tectum and compared it to activity of glia found in the regenerating visual system. Ablation of the tectum reduced glial incorporation of both [³H]thymidine and [³⁵S]methionine. Tectal ablation also led to nearly 80% reduction of amino acids incorporated by oligodendroglia as well as a decrease in the amount of newly synthetized protein found within multipotential glia and within cytoplasmic projections of astroglia. Since the tectal influence upon optic tract glia was detected at a time when tract and tectum are physically separated, we sought to determine if the optic tectum contained soluble glia-promoting factors. A soluble fraction recovered from tecta of the regenerating visual system increased amino acid incorporation within optic tract glia at 2-3-fold above preparations incubated with fractions from control, intact tecta. Comparisons of radiolabeled proteins separated by sodium dodecyl polyacrylamide gel electrophoresis from regenerating and factor-stimulated optic tract were similar and indicated that a soluble tectal fraction promoted biosynthesis of specific glial proteins. Our findings suggest that during regeneration of the goldfish visual system glia are influenced by humoral factor(s) released from the synaptic target site.