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

Abstract

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 hours. 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 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 suggests they were impaired in their capacity to grow to their correct targets.

Estudio Morfométrico del Nervio Óptico de Tiburoncito (Ariopsis seemanni)

“…En general las fibras del nervio óptico inervan el tectum óptico (TO) desde la región media hasta la posterior (Johnson et al, 1999). Específicamente la región ventronasal de la retina inerva el tercio medio o el tercio posterior del tectum óptico y la lamina óptica en goldfish (Dawson & Meyer, 2008). Esto sugiere que las diferentes subpoblaciones de fibras en el nervio óptico de A. seemanni podrían corresponder a la inervación en diferentes regiones del tectum, generando una topografía específica en esa estructura.…”

Cell lineage tracing techniques for the study of brain development and regeneration

“…For instance, DiI was used in studies of axonal regrowth following crush injury to entire CNS of embryonic rat (Saunders et al, 1992) or neonatal opossum (Treherne et al, 1992) maintained in culture. In vivo assays of axonal regeneration are also facilitated by the use of lipid‐soluble dyes such as those of optic fibers regenerate in the goldfish (Dawson and Meyer, 2001, 2008) and in the Xenopus tadpole (Vergara and Del Rio‐Tsonis, 2009).…”

Molecular imaging in the eye

“…Simultaneous imaging of RGCs and subpopulations of presynaptic amacrine interneurons over a period of days revealed that RGC dendrites targeted amacrine plexuses 20. The dynamic behaviour of axons can also be studied by intraretinal injection of the fluorescent carbocyanine dye DiI in goldfish and image acquisition using a fluorescence microscope equipped with rhodamine optics 21. In rodents, in vivo imaging of RGCs can be much more readily achieved by using transgenic mice that express CFP under the control of a Thy-1 promoter construct, and modified cSLO 22.…”