Ultrastructural pathology of neuronal membranes in the oedematous human cerebral cortex

Surgical biopsies of frontal, parietal and temporal regions of thirty two patients with clinical diagnosis of congenital hydrocephalus, brain trauma, tumours, and vascular anomalies were examined with the transmission electron microscope. The main goal was to study the submicroscopic alterations of somatodendritic, axonal, and synaptic plasma membranes, cytomembranes, and the cytoskeleton. In both, moderate and severe oedema, fragmentation of plasma membrane, enlargement and focal necrosis of rough endoplasmic cisterns and nuclear envelope, detachment of membrane-bound ribosomes and reduction of polysome were observed. The degenerated myelinated axons exhibited discontinuities of the axolemma, disorganisation of multiple myelin lamellae, myelin sheath vacuolization, and formation of myelin ovoids. In severe oedema, synaptic disassembly was frequently found characterized by separate pre- and postsynaptic endings and loss of perisynaptic glial ensheathment. Fragmented and intact microtubules and actin-like filaments also were distinguished. The alterations of plasma membranes and cytomembranes are related with the anoxic-ischaemic conditions of brain parenchyma. The role of free radical and lipid peroxidation, disturbed energy metabolism, altered metabolic cascades, excitotoxicity, protein aggregation, and presence of extracellular oedema fluid is discussed in relation with the derangement of neuronal membranes.