Regeneration of the retinotectal projection following compression onto a half tectum in goldfish

This study tested whether regeneration of the optic nerve following half-tectal compression in goldfish leads to the immediate reestablishment of the compressed projection or to an initial half map followed by the gradual compression. Half of the tectum was removed and the optic nerve crushed in large 12-18 cm goldfish which were kept at 20 degrees C and later mapped either in air or in water. At 35 to 41 days, the maps showed the presence of the nasal field projection and only the first 27 degrees of the temporal field. Most of the temporal field was represented after 200 days or more. After 253 to 343 days when the compression was largely complete, the optic nerve was recrushed. The projections mapped 35 to 41 days later were always compressed with up to 99% of the temporal field represented, as were projections regenerated at 28 degrees C and mapped at 23-25 days. Regeneration after compression restores the compressed projection, consistent with the concept of altered tectal markers.