Quantitative Morphology of Synaptic Plasticity in the Aging Brain

Quantitation of synaptic ultrastructural changes is of great importance in neurobiology, since merely qualitative alterations, if not extreme, are not readily detectable. In the present paper we discuss our previous and present findings on the number (numerical density: Nv), size (average length of the synaptic profiles: L) and surface contact area (surface density: Sv) of the synaptic junctions in aging rodent and human brains. We found that number and size of the synapses are in a close inverse relationship so as to maintain the total surface contact area among the nerve cells constant. These three parameters are closely related to each other, their quantitation may thus represent a reliable index of the morphological aspects of synaptic plasticity, i.e. the modification of ultrastructure occurring at synaptic membranes after transient changes in synaptic activity. During aging, the morphological plasticity of synapses appears to be seriously impaired: the number of synapses and the total surface contact area among the nerve cells are markedly reduced. However, old nerve cells seem to retain the ability to modify their synaptic endings and to partially compensate for the reduced surface density of the contact zones by expanding the average size of the persisting junctions. Our recent studies on synaptic plasticity in human brains from old and demented subjects showed that while the size of the synaptic contacts remains constant, the numerical and surface densities undergo a further decrease in demented brains relative to that in normal aging

Vitamin E Deficiency as a Model of Precocious Brain Aging: Assessment by X-Ray Microanalysis and Morphometry

Vitamin E (α-tocopherol) is a known biological antioxidant able to quench the lipid peroxidation chain and to protect the cellular structures (e.g., plasma membranes) from the attack of free radicals which are reported to play a primary role in aging. To assess whether the absence of α-tocopherol from the diet of young laboratory animals may be considered a reliable model of precocious brain aging, intracellular ionic content of brain cortex pyramidal cells, ultrastructural features of synaptic contact zones, synaptic mitochondria and perykarial mitochondria positive to the succlillc dehydrogenase (SDH) histochemical reaction with copper ferrocyanide have been investigated by X-ray microanalysis and computer-assisted morphometry in young, adult, old and 11-month-old vitamin E deficient rats. Our data document significant alterations of intracellular ionic content, synaptic contact areas and synaptic and perykarial mitochondria in aging. Vitamin E deficiency caused similar alterations in adult animals. Taking into account the known role of α-tocopherol in protecting the cellular membrane structure, we support that the common process underlying the changes found in aging and vitamin E deficiency is an excessive deterioration of the neuronal membrane