Differentiation-associated Na+-dependent inorganic phosphate cotransporter (DNPI) is a vesicular glutamate transporter in endocrine glutamatergic systems.

Immunohistochemical localization of D-aspartate in the rat pineal gland.

Interstitial cells in the pineal gland of the rat were characterized immunocytochemically using the monoclonal antibodies MRC OX-42 and ED1 for macrophages/microglia, and MRC OX-6, which recognizes major histocompatibility complex (MHC) class II antigen. A polyclonal antibody against GFAP was used to identify astrocytes. Cells immunopositive for OX-42 and/or ED1 were distributed throughout the gland; they extended processes primarily along the perivascular spaces and occasionally within the parenchyma of the gland. Ultrastructurally, these OX-42-positive cells were characterized by a nucleus with sparse heterochromatin and cytoplasmic vacuoles/lysosomes. Cells expressing MHC class II antigen had a distribution and morphology similar to OX-42-immunopositive cells, suggesting that pineal macrophages/microglia play a role as antigen-presenting cells. GFAP-positive astrocytes were concentrated at the proximal end of the pineal where the pineal stalk enters the gland. The occurrence of antigenpresenting cells in the circumventricular neuroendocrine gland has important functional implications as these cells may be mediators of neuroimmunomodulatory mechanisms, and involved in certain disease states such as autoimmune pinealitis.

Immunocytochemical and electron-microscopic characterization of macrophage/microglia cells and expression of class II major histocompatibility complex in the pineal gland of the rat

Immunoperoxidase methods for the demonstration of three glial antigens, vimentin, glial fibrillary acidic protein, and S-100 protein, were applied to routine-fixed paraffin sections of rat pineal gland. A pre-embedding electron microscope immunoperoxidase method was also used to study the ultrastructural localization of S-100 protein in pineal cells. Light and electron microscopic results showed the presence of these antigenic glial markers in the second pineal cell type. The term glial cell is proposed for the second of parenchymatous cell in rat pineal gland.

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Presence of glial cells in the rat pineal gland: A light and electron microscopic immunohistochemical study

A vesicular glutamate transporter (VGLUT) is responsible for the accumulation of l-glutamate in synaptic vesicles in glutamatergic neurons. Two isoforms, VGLUT1 and VGLUT2, have been identified, which are complementarily expressed in these neurons. Mammalian pinealocytes, endocrine cells for melatonin, are also glutamatergic in nature, accumulate l-glutamate in synaptic-like microvesicles (SLMVs), and secrete it through exocytosis. Although the storage of l-glutamate in SLMVs is mediated through a VGLUT, the molecular nature of the transporter is less understood. We recently observed that VGLUT2 is expressed in pinealocytes. In the present study, we show that pinealocytes also express VGLUT1. RT-PCR and northern blot analyses indicated expression of the VGLUT1 gene in pineal gland. Western blotting with specific antibodies against VGLUT1 indicated the presence of VGLUT1 in pineal gland. Indirect immunofluorescence microscopy with a section of pineal gland and cultured cells indicated that VGLUT1 and VGLUT2 are co-localized with process terminal regions of pinealocytes. Furthermore, immunoelectronmicroscopy as well as subcellular fractionation studies revealed that both VGLUT1 and VGLUT2 are specifically associated with SLMVs. These results indicate that both VGLUTs are responsible for storage of l-glutamate in SLMVs in pinealocytes. Pinealocytes are the first exception as to complementary expression of VGLUT1 and VGLUT2.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1471-4159.2003.01532.x

Co-expression of vesicular glutamate transporters (VGLUT1 and VGLUT2) and their association with synaptic-like microvesicles in rat pinealocytes

Antigenic markers characteristic of astrocytes and their differentiative states (i.e., glial fibrillary acidic protein (GFAP), vimentin, and M1 and C1 antigens) were investigated in the pineal gland of mouse and rat using double immunolabeling techniques. In both species the socalled interstitial cells as characterized by TEM were shown to be astrocytes, since they expressed vimentin, but neither fibronectin (a marker for fibroblasts and endothelial cells) nor the neuron-specific L1 antigen or tetanus toxin receptors. Subpopulations of vimentin-positive pineal astrocytes were also GFAP- and C1- antigen-positive. M1- antigenpositive cells were not detected.

P. Ziegelmüller

Papers

Glial cells in the pineal gland of mice and rats. A combined immunofluorescence and electron-microscopic study.