Non-N-methyl-D-aspartate glutamate receptors in glial cells and neurons of the pineal gland in a higher primate.

A role for glutamate in signalling mechanisms in the mammalian pineal gland is suggested by the high concentration of the transmitter in pinealocytes and the expression of glutamate receptor subunits in the rat gland. A single type of glutamate binding site has been characterized in the rat and bovine pineal gland, preferentially sensitive to the glutamate agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), a potent inhibitor of melatonin synthesis in vitro. In order to investigate the anatomical basis of a putative role of glutamate in the pineal gland of a higher primate, we performed an immunohistochemical analysis of the cellular localization of AMPA-type glutamate receptor subunits in the pineal gland of the macaque. Staining obtained with an antibody specific to GluR1 receptor subunit showed that this subunit is present in interstitial cells and astrocyte-like cells located in the parenchyma of the distal part of the gland. An antibody specific to GluR4 subunit stained astrocyte-like cells throughout the gland, however mainly in the proximal part, as well as a network of thin and long astrocytic-like processes located exclusively in the distal part of the gland. Staining obtained with an antibody recognizing both GluR2 and GluR3 subunits and the variant GluR4c exhibits a neuropilar-like pattern heterogeneously distributed throughout the gland.(ABSTRACT TRUNCATED AT 250 WORDS)