Reorganization of retinotectal projection following surgical operations on the optic tectum in goldfish

The results confirm that the remaining rostral half-tectum reacquires a complete visual projection from the whole retina about 90 days after excision of the caudal half of the tectum, and it is suggested that the reorganization of retinotectal projection is due to synaptic respecifications of individual tectal neurons in correct Retinotopic order.

Abstract

The pattern of neural reconnection between the retina and surgically operated tectum was studied in juvenile goldfish (8–11 cm long) with electrophysiological methods. The results confirm that the remaining rostral half-tectum reacquires a complete visual projection from the whole retina about 90 days after excision of the caudal half. The same reorganization of visual projection from the whole retina onto the rostral half-tectum was found to occur in the presence of the caudal half of the tectum, if the two halves were separated by a transverse surgical incision down to the level of the optic ventricle regardless of whether the contralateral optic nerve was left intact or crushed to regenerate. The reorganization of retinotectal projection was also found to occur biaxially along the mediolateral as well as the rostrocaudal axis of the tectum following excision of a caudomedial sector of the tectum. It is suggested that the reorganization of retinotectal projection is due to synaptic respecifications of individual tectal neurons in correct retinotopic order, and that the cellular discontinuity between the rostral and the caudal parts of the tectum is sufficient to induce the orderly synaptic respecifications in juvenile goldfish.