Supraependymal Cell Clusters Induced by ENU Treatment in Developing Rat Retina

Supraependymal cell clusters in the retina induced by treatment with ethylnitrosourea in fetal and. neonatal rats are described. Following the early cytotoxic effects of this drug on the matrix layer, the supraependymal cell clusters began to form a protrusion from the matrix layer into the intraretinal space through the defective portion of the outer limiting membrane. The supraependymal cell clusters consisted of matrix cells and neurons, or matrix cells, neurons, photoreceptor‐like cells, and glial cells depending on the time of treatment. The clusters became smaller in size, but they remained at least for 7 days after treatment. Our findings indicate that defect of the outer limiting membrane induced by the cytotoxic effect of ethylnitrosourea may be an essential factor for the formation of supraependymal cell clusters, and that the clusters can be regarded as a type of tissue malformation or dysontogenetic anomaly.