Endogenous gamma-L-glutamylglutamate is a partial agonist at the N-methyl-D-aspartate receptors in cultured cerebellar granule cells

Expression of gamma-glutamyl transpeptidase in mouse perivascular astrocytes and in a protoplasmic-like astroglial cell clone

Gamma-glutamyl transpeptidase (GGT) is known to be present in the central nervous system (CNS) but its cellular localization is still subject to controversy. In this report, we have investigated, with a specific antiserum, the immunolabelling pattern of GGT in the adult mouse CNS at the light and electron microscopic (EM) levels. At the optical level, GGT immunoreactivity ensheathes the majority of vessels in the grey matter. Immunoelectron microscopy shows that labelling is essentially due to the presence of GGT in the astrocytic endfeet which surround vessels. In addition, some pericytes and periendothelial cells are also clearly labelled. We then investigated GGT activity in astroglial cell clones which may represent the in vitro counterpart of the main astroglial cell types. The striking result is that a protoplasmic-like astroglial cell clone shows a noticeable GGT activity, while, in contrast, no activity was detected in the fibrous and the Golgi-Bergmann-like astroglial clones. Taken together, these data indicate that, in the mouse CNS, GGT is essentially present in protoplasmic astrocytes.