Growth dynamics and morphology of regenerating optic fibers in tectum are altered by injury conditions: An in vivo imaging study in goldfish

• Published in: Experimental neurology Vol. 210; no. 2; pp. 592 - 601
• Main Authors: Dawson, Amy J., Meyer, Ronald L.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-04-2008; Elsevier
• Subjects: Amino Acids; Animals; Axon; Biological and medical sciences; Carassius auratus; Diagnostic Imaging; Eye Enucleation - methods; Goldfish; Injuries of the nervous system and the skull. Diseases due to physical agents; Medical sciences; Nerve Regeneration - physiology; Neurology; Nonlinear Dynamics; Optic Nerve Injuries - pathology; Optic Nerve Injuries - physiopathology; Plasticity; Regeneration; Retina; Tectum; Tectum Mesencephali - pathology; Time Factors; Topography; Traumas. Diseases due to physical agents; Regeneration; BDNF; WGA-HRP; Topography; Plasticity; Axon; Retina; Tectum; Nervous system diseases; Growth; Central nervous system; Optic tectum; Encephalon; Eye; Visual system; Visual pathway; Morphology
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1016/j.expneurol.2007.12.006

The dynamic behavior of axons in systems that normally regenerate may provide clues for promoting regeneration in humans. When the optic nerve is severed in adult goldfish, all axons regenerate back to the tectum to reestablish accurate connections. In adult mammals, regeneration can be induced in optic and other axons but typically few fibers regrow and only for short distances. These conditions were mimicked in the adult goldfish by surgically deflecting 10–20% of optic fibers from one tectum into the opposite tectum which was denervated of all other optic fibers by removing its corresponding eye. At 21–63 days, DiI was microinjected into retina to label a few fibers and the fibers were visualized in the living fish for up to 5–7 h. The dynamic behavior and morphology of these regenerating deflected fibers were analyzed and compared to those regenerating following optic nerve crush. At 3–4 weeks, deflected fibers were found to form more branches and to maintain many more branches than crushed fibers. Although both deflected and crushed fibers exhibited stochastic growth and retraction, deflected fibers spent more time growing but grew for less distance. At 2 months, both deflected and crushed fibers became much more stable. These results show that the morphology and behavior of fibers regenerating into the same target tissue can be substantially altered by the injury conditions, that is, they show state-dependent plasticity. The morphology and behavior of the deflected fibers suggest they were impaired in their capacity to grow to their correct targets.