Aberrant growth of regenerating retinotectal axons subsequent to optic tract ablation in goldfish.

This study examined the effect of optic tract ablation on retinotectal fiber regeneration in goldfish. Approximately two-thirds of the left optic tract was removed, and, at various times post lesion (10-75 days), the course of regenerating retinotectal fibers was traced using horseradish peroxidase. In all experimental animals, axons were observed regenerating through the visual pathway but at the brachia most of the fibers were channeled through the ventral brachium. We present evidence that fibers in the ventral brachium originated from ganglion cells in all regions of retina and that these fibers grew almost exclusively into ventral half tectum even though some of these fibers would normally synapse in dorsal half tectum. These observations suggest that optic tract ablation does not prevent retinal fiber regeneration but results in aberrant growth through the brachia and significant inhibition of exploratory fiber growth within the tectum.