ENaC γ-expressing astrocytes in the circumventricular organs, white matter, and
ventral medullary surface: sites for Na+ regulation by glial cells.
J Chem Neuroanat 2013;
53:72-80. [PMID:
24145067 DOI:
10.1016/j.jchemneu.2013.10.002]
[Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Accepted: 10/02/2013] [Indexed: 12/19/2022]
Abstract
Using a double immunofluorescence procedure, we report the discovery of a novel group of fibrous astrocytes that co-express epithelial sodium channel (ENaC) γ-subunit protein along with glial acidic fibrillary protein (GFAP). These cells are concentrated along the borders of the sensory circumventricular organs (CVOs), embedded in the white matter (e.g., optic nerve/chiasm, anterior commissure, corpus callosum, pyramidal tract) and are components of the pia mater. In the CVOs, a compact collection of ENaC γ-immunoreactive glial fibers form the lamina terminalis immediately rostral to the organum vasculosum of the lamina terminalis (OVLT). Astrocyte processes can be traced into the median preoptic nucleus - a region implicated in regulation of sodium homeostasis. In the subfornical organ (SFO), ENaC γ-GFAP astrocytes lie in its lateral border, but not in the ventromedial core. In the area postrema (AP), a dense ENaC γ-GFAP glial fibers form the interface between the AP and nucleus tractus solitarius; this area is termed the subpostremal region. Antibodies against the ENaC α- or β-subunit proteins do not immunostain these regions. In contrast, the antibodies against the ENaC γ-subunit protein react weakly with neuronal cell bodies in the CVOs. Besides affecting glial-neural functions in the CVOs, the astrocytes found in the white matter may affect saltatory nerve conduction, serving as a sodium buffer. The ENaC γ-expressing astrocytes of the ventral medulla send processes into the raphe pallidus which intermingle with the serotoninergic (5-HT) neurons found in this region as well as with the other nearby 5-HT neurons distributed along ventral medullary surface.
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