Ultrastructure of non-myelinated neurons during energy deprivation

This paper examines the neuropathology of oxygen-glucose deprivation uncomplicated by stagnant conditions. Rabbit vagus nerves were pulled into a multi-compartment perfusion chamber, stimulated five times per second and deprived of energy by substituting nitrogen and deoxyglucose for oxygen and glucose in the Locke's perfusate. After incubation the compartments were perfused with gluteraldehyde solution, and the nerves were prepared for electron microscopy. Fixation in the compartments ensured precise cross and longitudinal sections which permitted quantitative comparisons. Although the action potentials ceased in 45 min, 1 h of energy deprivation did not significantly affect the ultrastructure. After 2 h of deprivation the axons were smaller and flattened and microtubules appeared packed together. In the smallest axons the microtubules were gone, the neurofilaments were compacted and the few mitochondria had a dense, homogenous appearance. By 4 h the shrinking was extreme, yet 8% were swollen much larger than any of the controls. Longitudinal views showed these ballooned areas were greatly expanded regions of the smallest axons. Both tiny and huge regions were devoid of microtubules and the swollen axons contained expanded mitochondria. Calcium is indirectly implicated in the pathogenesis by the concurrence of mitochondrial alteration as the microtubules disappear coupled with the known role of mitochondria in calcium regulation and the reported effect of high calcium on microtubual dissociation. It is suggested that axons first shrink as osmotically active molecules are used or washed out. After a time without energy the mitochondria can no longer regulate the intracellular calcium, microtubules dissociate, and calcium-activated phospholipases create osmotically active molecules. Finally, high-amplitude, disruptive swelling occurs.