Section 7
Chapter 6,247

Quantitative ultrastructural changes in rat cortical synapses during early adulthood mid adulthood and late adulthood

Adams, I.; Jones, D.G.

Brain Research 239(2): 349-364


ISSN/ISBN: 0006-8993
Accession: 006246150

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Quantitative ultrastructural analysis of rat parietal cortex was undertaken to determine the nature of the synaptic changes occurring in the molecular layer over a series of ages in early (3 mo.), mid- (6 and 10 mo.) and late (17 mo.) adulthood. The total number of synapses remained constant until 10 mo. of age, but decreased significantly by 17 mo. Asymmetrical synapses on dendritic shafts were lost earlier (by 6 mo.) than asymmetrical synapses on dendritic spines (by 17 mo.). Symmetrical axodendritic synapses remained constant throughout adulthood. Analysis of synaptic terminal parameters revealed the following. Both individual and total presynaptic terminal areas decreased over the age range studied. Individual and total postsynaptic terminal areas, however, remained constant over the 3-17 mo. period. Positive correlations were obtained for the relationships between presynaptic terminal area and both age and synaptic vesicle number. The presynaptic terminal area was largest and contained the greatest number of vesicles at 3 mo. of age. This age was characterized by the least numbers of mitochondria in the presynaptic terminal and spine apparatus in the postsynaptic terminal. The vacuolar and tubular cisternae of the presynaptic terminal were considerably reduced at 17 mo. In the molecular layer of the cerebral cortex the period of adulthood is characterized by a diversity of synaptic changes. The 3-mo. age may reflect the end of the developmental phase and may be marked by changes in synaptic functional activity. The asymmetrical axodendritic synapses may constitute an intermediate form of synapse, capable of being transformed into axospinous synapses as dendritic spines continue to be formed in the adult.

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