[Presynaptic terminals in the sensorimotor area of the cerebral cortex in old laboratory rats]

In male laboratory rats, Wistar strain, 2 and a half years old, quantitative morphometric analysis of synapses (type I after to Gray) from the second layer of the sensorimotor area of the neocortical region was performed. Evidence was provided of enlargement of the area of presynaptic formations, their circumference and of prolongation of the active zone of the synapse. The absolute number of agranular synaptic vesicles does not change, however, the number of vesicles per area unit declines (1 micron 2). This change was proved in all regions of the presynaptic ending. The enlargement of the area of synaptic endings is discussed in relation to possible shifts of water and electrolytes between the extracellular and intracellular space as a result of ageing of nervous tissue. The authors discuss also the passive change caused by a decrease of neuropil structures and narrowing of the extracellular space. The relative decline of the number of synaptic vesicles in the entire synapse and thus in the vicinity of the active zone is taken to be the morphological basis of a certain restriction of synaptic transmission in the sensorimotor area of the cortex in old age.