The paired neuroglial and interglial membranes in the crayfish stretch receptor and their local disorganization

The paired neuronal and glial membranes, or interglial membranes, which are separated by the narrow layer of the extracellular medium, are involved in intercellular communications. In the crayfish stretch receptor, the paired neuroglial membranes contain thin protein bridges (septate junctions) that maintain the intermembrane gap. In some places the paired membranes are locally disorganized. In the altered regions, they comprise the diffuse material in which a few 10-15 nm vesicles are embedded. The development of these defects can lead to formation of 20-30 nm vesicles and perforations in the paired membranes. The presence of such holes can, in principle, disturb ionic gradients and neuronal activity. However, a free passage between contacting neurons and glia is prevented by the diffuse proteolipid material (the product of the membrane disorganization) that seals perforations. As a result, the neuroglial border does not lose its integrity and impermeability for ions so that the sensory neurons save the capability for prolonged regular firing. Unlike the neuroglial border, some perforations in the paired glia-glial membranes are not sealed. This can create the interglial syncytial connections providing the shortcut pathway for transport of ions and metabolites across the glial layers in the crayfish stretch receptor.