Morphological changes in the cat cerebral cortex produced by superfusion of ouabain

The morphological changes following superfusion of the cat cerebral cortex with ouabain were studied. Autoradiography of [3H]ouabain was performed to study drug distribution. The resulting lesion consists of an upper vacuolated layer which is distinctly separated from an underlying region containing dark neurones. Ouabain is confined to the vacuolated layer. Swelling of apical dendrites and many presynaptic terminals are the main morphological changes occurring in the vacuolar layer. Depletion of synaptic vesicles, clustering of vesicles around the synaptic membrane, and the production of coated vesicles and cisternae are further changes found within presynaptic endings. Whilst swelling of fibrous astrocytes within the glialimitans occurs, this is not true of astrocytic processes elsewhere in ouabain exposed regions. Regions containing dark neurones are characterised by a general swelling of astroglial processes. The results strongly suggest that apical dendrites and presynaptic endings possess high activities of Na+, K+-ATPase whereas the activity on astroglial processes within the neuropil is relatively low. Astroglial swelling in areas of dark neurones is produced by some change in the chemical milieu surrounding the processes which appears unrelated to Na+, K+-ATPase inhibition.