Aging: Extracellular Space

Abstract

The extracellular space (ECS) is the microenvironment of the nerve cells and an important communication channel, allowing for long-distance extrasynaptic ‘volume’ communication by the diffusion of neuroactive substances between cells. The degree of impaired learning in aged rats and mice correlates, first, with a decrease in the ECS volume and a loss of diffusion anisotropy in the hippocampus, and, second, with structural changes, including the disorganization of astrocytic processes and a reduction of ECS matrix molecules, without a significant loss of neurons. Changes in diffusion parameters have also been found in an animal model of Alzheimer’s disease. The changes in hippocampal diffusion parameters are more evident in aged animals with severe learning deficits and could therefore account for learning impairment, due to their effect on extrasynaptic transmission.