Retinotectal reorganization in goldfish—II. Effects of partial tectal ablation and constant light on the retina

Abstract

In a proportion of small fish, after removal of half the tectum, exposure to constant light induces compression of the retinotectal projection. In contrast, it prevents compression in large fish. Loss of rod photoreceptors occurs in both small and large fish kept in constant light. This was not sufficient to induce compression. In large fish removal of half the tectum followed by exposure either to light/dark or to constant light has no consistent effect on the number of retinal ganglion cells. In small fish the removal of half the tectum alone causes a loss of ganglion cells in the eye projecting to the operated tectum. This in itself was not associated with compression. In half the small fish, exposure to constant light following the removal of half the tectum produced an even greater loss of ganglion cells in the eye projecting to the operated tectum. This increased loss of ganglion cells may be sufficient to induce compression, probably by creating vacant synaptic sites in the tectum. That only a proportion of fish show increased loss of cells correlates with the finding that only a proportion undergo compression in constant light.