Astrocytes In Elderly Individuals

Astrocytes in elderly individuals have large cell bodies and robust protrusions, particularly those found in the NFL. In the group of subjects aged over 60 years, the astrocytes showed a higher glial fibrillar acidic protein (GFAP) immunoreactivity with respect to the younger subjects, particularly in the NFL. This observation has been confirmed by electron microscopy, which showed a higher density of glial filaments (formed by GFAP) in the astrocyte cytoplasm of the elderly group. In the NFL the lack of GFAP(+) signal between the astrocyte bundles indicates that in this layer the astrocytes lose their protrusions. Occasionally GFAP(+) organelles are found in the CGL and NFL; these correspond to decayed astrocytes. The perivasal astrocytes have few thin protrusions and form a thinner astroglial sheath than in younger individuals. Sporadically, reactive astrocytes are found. The honeycomb structure is not easily distinguished in the CGL, and the gaps in the astroglial plexus have variable forms (circular, square, rectangular); the dimensions, however, are larger than those in younger subjects in both zone A (nearer to the optic disk) and zone B (closer to the periphery). The number of gaps in the astroglial honeycomb plexus in the CGL is lower in the 60 to 89 age group. This signifies that the gaps are larger due to the disappearance of astrocytes from the vessel walls and the astroglial protrusions that divide the gaps. The reduction in the number of astrocytes increases with age, as is shown by comparing people between 60 and 79 and those over 80. The comparison between young and elderly retinas has therefore again shown that aging causes numerous changes to the retinal astrocytes. There is an increase in the number of intracytoplasmatic organelles (mitochondria, ribosomes, polyribosomes, wrinkled endo-plasmatic reticulum) due to higher cellular activity, an increase in lysosomes and dense bodies (which increase also inside the Miiller cells), an increase of the glial intermediate filaments, a thickening of the inner limiting membrane whose constituents are less homogeneous, and the space between the glial protrusions and the basal membrane of the inner limiting membrane increases.

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