Synaptic morphology and cytoplasmic densities: Rapid post-mortem effects

In the study of nervous tissue, the shift from the living state to the post-mortem condition affects the ultrastructure of the neuron in ways incompletely understood. We have observed rapid post-mortem changes associated with the synaptic region in the molecular layer of the rat dentate gyrus. These changes are evident in tissue taken from anesthetized animals in which perfusion was begun while the heart was beating but breathing had stopped. Such alterations were rarely in evidence if perfusion was started while the animal was breathing, either with or without artificial means. The following morphological alterations were observed: (a) an increase in spherical electron densities seen near the synapse as well as in the perinuclear cytoplasm; (b) a variation in the amount of density attached to the thickening of post-synaptic membrane; (c) a change in the curvature of the synaptic cleft. Because of these rapid alterations, caution is recommended in the interpretation of the in vivo morphology of the synapse and associated densities.