Neuroglial cells: morphological changes during normal aging
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REVIEW
Neuroglial cells: morphological changes during normal aging Ennio Pannese
Received: 21 October 2012 / Accepted: 6 December 2012 / Published online: 27 December 2012 Ó Accademia Nazionale dei Lincei 2012
Abstract Morphological changes in neuroglial cells of the central nervous system during aging include astrocytic hypertrophy, myelin alterations, shape changes of microglial cells, and decreased volume of the extracellular space. Age-related changes in neuroglial cells of the peripheral nervous system include myelin alterations, decrease in volume of perineuronal satellite cell sheaths, and increased surface area of sensory ganglion neurons unprotected by the satellite cell envelopment. Some of these changes probably contribute to the behavioral impairment and cognitive decline that often accompany normal aging. Keywords Astrocytes Oligodendrocytes Microglial cells Schwann cells Perineuronal satellite cells Myelin
1 Introduction For over a century it was thought that neuroglia exercised the passive role of simply filling the gaps between neurons. However, work over the last 30 years indicates that many neural activities are the result of a collaboration between neurons and glia. For this reason, neuroglial cells cannot be neglected when surveying morphological changes occurring at the cellular level in the nervous system during normal aging. Changes in nerve cells were examined in a previous short review (Pannese 2011). In the present paper, age-related changes in neuroglial cells are reviewed.
E. Pannese (&) Viale San Michele del Carso 15, 20144 Milan, Italy e-mail: [email protected]
2 Cells in contact with the cerebrospinal fluid Little information is available on the age-related changes in these cells. In old age, the cilia of ependymal cells are reduced in density, and in restricted regions these cells may be entirely lost. At these sites, the subependymal astrocytes may become hypertrophic. Biondi bodies (see the next paragraph) have been described in the ependymal cells of aged humans. Age-related changes documented in tanycytes are the accumulation in the cytoplasm of lipid droplets and of bodies consisting of a dense material and myelin figures. In aged humans, the choroidal epithelium cells may become flattened and may contain iron-positive inclusions and Biondi bodies (Biondi 1933). Electron microscope studies (Bargmann and Katritsis 1966; Oksche and Kirschstein 1972; Wen et al. 1999) have shown that each Biondi body consists of a bundle of filaments (8–10 nm in thickness) among which small lipid droplets and dense granules are interspersed. Lipofuscin granules may also be associated with these structures. Origin and significance of Biondi bodies are unknown.
3 Astrocytes Studies in various species and different regions of the nervous system have shown that the mean number of astrocytes does not change significantly with age [e.g., rat and mouse hippocampus (Lindsey et al. 1979; Bhatnagar et al. 1997; Long et al. 1998), rat auditory cortex (Vaughan and Peters 1974), human neocort
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