A sensitive period for ganglion cell degeneration and the formation of aberrant retino-fugal connections following tectal lesions in rats.

Rats of 0, 3, 5, 10 and 30 days of age received unilateral tectal lesions. After surviving for 150 days the retinal ganglion cell layer of the contralateral eye was examined for evidence of a ganglion cell loss. The retino-fugal projections of the eye contralateral to the lesion were studied in autoradiographs. In the animals operated at 0 days of age, 33% of the ganglion cells had degenerated but in animals operated at 5 days of age, 67% of the ganglion cells had degenerated. The animals operated at 30 days of age show no significant cell loss. An aberrant retinal projection to the lateral posterior nucleus of the thalamus was found only in animals operated at 0 and 3 days of age. The retinal projection to the thalamus was investigated in normal rats of 0, 3, 5 and 10 days of age using the anterograde transport of horseradish peroxidase. There was a conspicuous projection to the lateral posterior nucleus in animals of 0 and 3 days of age, but in the 5-day-old rat the retinal projection to the lateral posterior nucleus was very small and similar to the adult pattern. We conclude that transecting the tectal terminals of retinal ganglion cells causes the ganglion cells to degenerate, unless they are old enough to have formed sustaining collaterals. In addition, the tectal lesion removes a major tectal input to the lateral posterior nucleus and, if carried out within the first few days, leads to the preservation of the normally transient retinal projection to the lateral posterior nucleus, presumably by reducing competition between axon terminals.