Axonal rearrangement without reexpression of a growth associated marker: evidence from the compression of the retinotectal system in adult goldfish.

PURPOSE: Growing axons express a number of proteins associated with axonal growth which are thought to be critical for regeneration and sprouting. Whether these proteins are expressed during injury-induced axonal remodeling is tested in this paper.

METHODS

The posterior half of the adult goldfish tectum was removed leaving the anterior half intact. This causes optic fibers from nasal retina, which project to posterior tectum, to displace temporal fibers from the anterior remnant and form a compressed retinotopic projection of the entire retina onto the anterior tectum. Immunohistochemistry using an antibody shown here to recognize growing and regenerating fibers in goldfish was used to monitor optic fibers.

RESULTS

As expected, surgery induced reactivity in the axotomized nasal axons peaking at 1 month which returned to normal at 2 months when compression was completed. Unexpectedly, axons from temporal retina showed no detectable reactivity even though they were induced to grow anteriorly by the invading nasal fibers.

CONCLUSIONS

Extensive axonal remodeling and synaptic rearrangement can occur without reentering the growth state associated with axonal growth and regeneration.