Glial cells produce and release neuropeptides

All types of glial cells produce and release neuropeptides (Table 5.4). The production of neuropeptides is highly region specific, and in many cases developmentally regulated. In particular, astroglial cells synthesize many types of opioid peptides such as enkephalins, which are involved in the regulation of cell proliferation and dendritic growth in the CNS. Similarly, opioids (proenkephalin and prodynorphin) are expressed in cells of the oligodendrocyte lineage, and may be involved in regulation of their development. Astrocytes in the cortex and cerebellum produce atrial natriuretic peptide, and are the main source of brain angiotensinogen; both peptides are involved in the regulation of brain water homeostasis. Some perivas-cular astrocytes also produce vasoactive intestinal polypeptide (VIP), which is involved in the regulation of the brain microcirculation. Neuropeptide Y (NPY) is heavily expressed by ensheathing cells of olfactory axons (olfactory ensheathing cells), where it is involved in promoting the growth of axons from olfactory epithelium to the olfactory bulb; similarly NPY is found in developing Schwann cells. The mechanisms of neuropeptide release from glial cells remain obscure. In some cases, it may involve exocytosis. This, for example, has been demonstrated for NPY, which is accumulated in vesicles present in olfactory ensheathing cells, and these vesicles can undergo Ca2+-regulated exocytosis.

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CH05 GENERAL PHYSIOLOGY OF GLIAL CELLS

Table 5.4

Neuropeptides production and release

in glial cells

Neuropeptide

Glial cell type

Function

Neuropeptide Y (NPY)

Ensheathing cells of the

Targeting axons to

olfactory system

appropriate destination

Developing Schwann cells

Opioids (enkephalin,

Astrocytes

Regulation of cell

proenkephalins, dynorphin)

Oligodendrocyte precursors

differentiation; control

over dendritic growth

Angiotensinogen

Astrocytes in cortex and

Part of brain

cerebellum

renin-angiotensin system,

regulation of water/ion

homeostasis in the CNS

Atrial natriuretic peptide

Astrocytes, Bergmann glia

Regulation of water/ion

(ANP)

homeostasis in the CNS

Vasoactive intestinal peptide Astrocytes

Regulation of brain

(VIP)

Pituicytes

circulation (?)

Substance P

Astrocytes

Neuroinflammatory/damage

Microglia

mediator

Galanin

Oligodendrocyte precursors

Expression of galanin is

controlled by thyroid

hormone; galanin

may be involved in

regulation of growth and

differentiation of neurones

and oligodendrocytes

Carnosin

Astrocytes

??

Tanycytes

Ependyma

Oligodendrocytes

Nociceptin

Astrocytes

??

Oxytocin and vasopressin

Pituicytes

??

Somatostatin

Astrocytes

??

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