The effects of early tectal lesions on development in the retinal gonglion cell layer of chick embryos.

The possibility that the arrival of retinal ganglion cell axons in their efferent target field could influence the subsequent progress of cytomorphogenesis in the ganglion cells was tested by destroying all or portions of the primordial optic tectum at four or five days of incubation. The lesions were made essentially prior to the outgrowth of axons from the eye. Complete bilateral or unilateral destruction of the primordial tectal field did not detectably alter the morphogenesis of the inner retina or of the ganglion cells until 11 days of incubation. After this time, extensive loss of ganglion cells occurred within the retinas contralateral to the projection fields that were destroyed. The cytology of this degeneration is described as seen with the light and electron microscope. After smaller lesions involving the anterior or posterior half-tectum on one side, however, variable results occurred both in tectal development and in the retinal locus of ganglion cell degeneration observed in flat mount preparations. Many partial or punctate lesions, in fact, resulted in no detectable loss of cells from the ganglion cell layer. These results are discussed in regard to specification and possible regulatory capabilities of the tectum. Cell death in normal retinas, not previously reported in the chick, is also considered in relation to the experimental results.