Morphometric studies of biological changes in synapses of the human caudate nucleus

: In the adult the caudate nucleus decreases with increasing age. Light microscopic measurements result in smaller sized neurons and a reduced neuropil in the aged. Comparable to a sintering, nerve cells move nearer, and in consequence, their density increases. The total number of nerve cells, however, does not change remarkably. Using electronmicroscopic methods the aging of synapses was morphometrically examined: Blocks of the caudate nucleus were cut out of formalin-fixed brains from 43 males who had died between the 22nd and 102nd year of age without any neurological symptoms. The blocks were contrasted with EPTA (ethanolic phosphotungstic acid) and embedded in araldite. Though the whole tissue was autolytic, presynaptic and postsynaptic densities were well-preserved and clearly visible. Their numbers and sizes were measured with semiautomatic procedures. The regression analysis shows a significant decrease of the density of synapses with increasing age. The aging of the human caudate nucleus is characterized by a decrease of its volume, by a reduction of the size of neuronal perikarya, and a diminution of the number of synapses per neuron. But the total number of nerve cells remains nearly constant.