Extracellular space in the developing retina assessed by electron microscopy: laminar and topographic distribution

The extent of extracellular space (ECS) in the developing retina of the cat has been measured by electron microscopy in material fixed using techniques developed by others to preserve ECS. ECS is generally greater in foetal than in adult material. It is particularly marked in the plexiform layers of retina at the time of synaptogenesis and in the axon layer at the time of axon growth. The changes in ECS occur first in the central retina, and spread to the periphery. These observations suggest that the high volumes of ECS found in the foetus are not artefactual, but accompany and may play a role in developmental processes.