Extracellular Space in Central Nervous System

Abstract

The ultrastructures of the cerebellar cortex in living mice were investigated using the “in vivo cryotechnique” (IVCT). Electron microscopic observation with IVCT revealed that large extracellular spaces (ECS) were clearly observed among profiles of neurons and glia in molecular and Purkinje cell layers of the mouse cerebellum. The ECS were significantly reduced by prolonged ischemia/anoxia, since the ECS were smaller in tissue specimens obtained with IVCT following 8 min ischemia or the conventional quick-freezing method of resected fresh tissues. The parallel fibers observed with IVCT after short period of ischemia were slightly larger than those without ischemia, indicating cellular swelling after ischemia/anoxia. ECS were also abundant around synaptic terminals, which were totally or partially covered with glial processes, and the ECS sizes of opened (not covered with glial processes) and enclosed (covered with glial processes) synapses are estimated to be similar. These findings indicate that IVCT is useful to analyze ECS morphology in the central nervous system. The abundant ECS would allow morphological changes of neuronal and glial cells involved in dynamic remodeling and signal transduction of synapses.