Use of a lectin-peroxidase conjugate (WGA-HRP) to assess the retinotopic precision of goldfish optic terminals.

The lectin wheat-germ agglutinin (WGA), conjugated to horseradish peroxidase (HRP), is an effective tracer for goldfish optic axons. Under suitable conditions, WGA-HRP injected iontophoretically into the normal goldfish tectum is taken up by retinotopic optic terminals (but not by axons of passage) and labels a small, discoid patch of retinal ganglion cells. Under identical conditions, unconjugated HRP is mainly taken up by injured axons of passage. WGA-HRP injected into the tectum after regeneration of the contralateral optic nerve again labels a small patch of ganglion cells, demonstrating the extent to which regenerated terminals are also retinotopic.