Morphologic analysis of axo-glial membrane specializations in the demyelinated central nervous system

Axo-glial membrane specializations, occurring in demyelinated spinal cord lesions in guinea pigs with chronic, relapsing experimental allergic encephalitis (EAE) and a case of multiple sclerosis (MS) between naked axons and scarring astrocytes, have been analyzed in transverse and longitudinal sections by transmission electron microscopy. The most common axo-glial specialization was of the desmosome-type and was plaque-like and punctate. It was not related to the region of subaxolemmal densification at the nodes of Ranvier. Synapse-like and gap junctions were also seen, but rarely, between naked axons and astrocytes in chronic EAE. In MS, only desmosome-like specializations were encountered between axons and glia and they were less extensive than in the guinea pig material. Surprisingly, similar chronically demyelinated lesions in the optic nerves of guinea pigs, failed to display axo-glial membrane specializations. It is speculated that their presence in spinal cord lesions is related to the proximity of gray matter and is of relevance to regeneration.