Vesicular inhibitory amino acid transporter is expressed in γ-aminobutyric acid (GABA)-containing astrocytes in rat pineal glands

γ-Aminobutyric acid (GABA) is an inhibitory amino acid and acts as an intercellular transmitter in the central nervous system and peripheral tissues. In pineal glands, GABA is supposed to be a paracrine-like modulator of secretion of melatonin, although its mode of action, especially the sites of GABA signal appearance, is unknown. Vesicular inhibitory amino acid transporter (VIAAT) is a potential marker for the GABAergic phenotype. Here we presented evidence that VIAAT is expressed in GFAP-expressing astrocytes and a subpopulation of OX42-expressing microglia, but not in pinealocytes in cultured cells of rat pineal glands. The VIAAT-expressing cells also exhibit GABA immunoreactivity. Essentially the same results were obtained for pineal glands. These results suggest that GABA is stored and secreted from astrocytes and a subpopulation of microglia in pineal glands.