Compensatory enlargement of synaptic size in aging and senile dementia.

Synaptic contact zones in the dentate gyrus supragranular layer and cerebellar glomeruli of autoptic samples from adult, old and demented patients have been investigated by means of computer-assisted morphometric techniques. In physiological aging and senile dementia, the synaptic average area was significantly increased as compared with adult values in both the CNS areas investigated. Conversely, the number of contacts and their total surface contact area per unit volume of tissue were decreased. In animal models, the enlarged contact zones are reported to undergo perforations and splitting to modify synaptic connectivity. As against these assumptions, the increased synaptic size observed in our study appears to represent a compensative reaction of old and demented CNS to counteract the decrease in number and total contact area of the synaptic junctions.