Time course and pattern of optic fiber regeneration following tectal lobe removal in the goldfish.

Following single tectal lobe removal in the adult goldfish, Carassius auratus, the pattern of regeneration of the optic fibers which had previously projected to that tectum was examined at 1, 2, 4, 6, 8, 10, and 12 weeks postoperative using 3H-proline radioautography. We found that regenerating optic fibers grew across the midline through the transverse, minor, horizontal, and posterior commissures to innervate the remaining tectum. At early postoperative times innervation of the tectum was continuous, while later, the regenerating fibers segregated into discrete patches in the superficial layers of the tectum. In addition, regenerating fibers also grew into non-optic centers/pathways such as the habenula, the fasciculus retroflexus, the forebrain, the torus semicircularis, the valvula and corpus cerebelli, the hypothalamus, and the medulla. While optic fibers were no longer apparent in the habenula and the fasciculus retroflexus after 2 weeks postoperative, all other structures were still occupied by the fibers at 12 weeks postoperative. Since most of the innervated pathways were either tectal efferent pathways, which should contain degenerating debris and proliferating glial cells after the tectal removal, or pathways closely associated with traumatized areas, we suggest that degenerating axonal debris and proliferating glia may play an important role in guiding regenerating fibers in this system.