Neuronal and neuroglial responses following retinal lesions in the neonatal rats

Lesions were produced in the nasal-superior quadrant of rat retinas at 1 day postnatal. Both the optic fiber and ganglion cell layers were destroyed at the lesion site. Retrograde changes in the more peripherally located ganglion cell bodies, their optic fibers, and neuroglia were monitored by light and electron microscopy. No optic fibers remained in the region peripheral to the lesion site after 2 days postoperative (DPO). Neither regenerative sprouting nor axonal ingrowth from late-maturing ganglion cells in the retinal periphery was observed. Cell death of the large and the majority of medium ganglion cell bodies was very rapid as was clearing of the degeneration products. These processes peaked at 1 DPO and were complete by 2 DPO. Microglia and Mueller cell cytoplasm actively phagocytized degenerating ganglion cell bodies and their optic fibers. A stable population of cell bodies in the ganglion cell layer peripheral to the lesion remained intact from 2 DOP to 21 DPO. The surviving somata were consistently 65% of the control ganglion cell population, and they remained after their axons had degenerated. The cell bodies measured 6-12.1 micron in diameter, a range which included the small cell population and a few of the medium cells. Dendritic patterning, used to designate ganglion cell types, corroborated their classification as small and medium ganglion cells. Morphological changes in these perikarya due to axotomy were limited to a mild chromatolytic response.