Changes in the synapses in the parietal cortex of senescent rats.

Quantitative parameters characterizing the density of the synapses, the pre- and postsynaptic elements, and the synaptic contact zones (SCZ) in the parietal cortex of young adult (3-month-old) and aged rats (24 months) were investigated using an automated computer system. A big loss of axospinous, but not of axodendritic synapses, was observed in the aged rats. The parameters for the synaptic vesicles and SCZ were changed also only in the axospinous synapses. The changes in the quantitative parameters are accompanied by changes in the structure of synapses. The structural changes may be considered as being degenerative and regenerative.