Ultrastructural Changes in the Penumbra of the Local Cerebral Infarction in Rats.

We studied changes in the ultrastructure of synapses and myelin nerve fibers that develop in the penumbra in 4 and 12 h and 2 and 4 days after modeling infarction in the frontoparietal cortex in rats. Ischemic stroke was induced by injection of a photosensitive dye into their bloodstream followed by illumination of the brain surface with a halogen lamp. Visible ultrastructural changes were observed in the penumbra zone, namely in the axodendritic and axospinous synapses; they consisted in polymorphism and disorganization of synaptic vesicles, mitochondrial swelling, swelling and vacuolization of the postsynaptic fragments of dendrites, and shortening and osmiophilia of the active zone. In the presynaptic terminals, clear-cut signs of transformation were observed only in 2 and 4 days after infarction modeling. These terminals were located at the ends of the degenerated myelinated axons of necrotic neurons. These findings demonstrate irreversible changes in the ultrastructure of synapses in the penumbra in 2-4 days after infarction and indicate the necessity of early treatment of strokes.