Bidirectional axonal transport of glycoproteins in goldfish optic nerve
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The goldfish visual system was used to study the relationships between anterograde and retrograde transport of axonal glycoproteins. After intraocular injection of radioactive glucosamine, determinations were made of the normal time course of appearance of labeled glycoproteins in the optic nerve and tectum and of their time course of accumulation on both sides of an optic nerve crush. The labeled glycoproteins, transported at a maximum velocity of about 80 mm/day, continued to pass through the optic nerve in significant amounts for as long as 24 h after the injection, with a maximum at about 6 to 14 h. Retrograde transport of labeled materials back from the optic tectum to the same point in the nerve began about 5 h later, indicating a minimum possible retrograde velocity of about 36 mm/day and a maximum possible lag time in the axon terminals (with the assumption of equal retrograde and anterograde velocities) of 1 to 2 h. When delivery of glycoproteins from the retina to the optic tectum was interrupted by a nerve crush 8 h after injection, a component with rapid turnover in the tectum was revealed having a half-life of not more than 6 h. At least 40% of this turnover could be attributed to retrograde transport. The amount of labeled glycoprotein transported in a retrograde direction 8 to 10 h after injection was greatly elevated in regenerating axons 2 weeks after the optic tract was cut. © 1982.
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