IMAGING OF INDIVIDUAL NORMAL AND REGENERATING OPTIC FIBERS IN THE BRAIN OF LIVING ADULT GOLDFISH

Retinal arbors in the tectum of living adult goldfish were imaged to d etermine whether the structural remodelling and refinement that occurs during development continues in adulthood. Individual optic fibers we re labelled by making small injections of the lipophilic fluorescent d ye DiI into ventral retina and viewing the exposed tectum through a fl uorescence microscope equipped with a cooled CCD camera. Arbors were i maged in the living fish every 30-60 minutes for up to 7 hours. Normal adult goldfish showed no evidence of arbor remodelling during this pe riod, though dynamic movements of varicosities present along axon segm ents were observed. For comparison, regenerating optic fibers were sim ilarly imaged in fish that had undergone optic nerve crush 2-6 weeks p reviously. In these fish, dynamic structural changes were seen, includ ing branch remodelling, extension and retraction of growth cones, and movement of varicosities. (C) 1994 Wiley-Liss, Inc.