Cerebral Cortex, Vol. 12, No. 5, 515-525,
May 2002
© 2002 Oxford University Press
Similar Perisynaptic Glial Localization for the Na+,K+-ATPase 
2 Subunit and the Glutamate Transporters GLAST and GLT-1 in the Rat Somatosensory Cortex
Laboratory of Cerebrovascular Research, Montreal Neurological Institute, McGill University, 3801 University Street, Montréal, Québec, Canada, H3A 2B4 and , 1 Institut de Physiologie, Université de Lausanne, 7 rue du Bugnon, 1005 Lausanne, Switzerland
Professor Edith Hamel, Montreal Neurological Institute, 3801 University Street, Room 748, Montréal, QC, Canada H3A 2B4. Email: edith.hamel{at}mcgill.ca.
Several isoenzymes of the Na+,K+-ATPase are expressed in brain but their specific roles are poorly understood. Recently, it was suggested that an isoenzyme of the Na+,K+-ATPase containing the 
2 subunit, together with the glutamate transporters GLAST and GLT-1, participate in a coupling mechanism between neuronal activity and energy metabolism taking place in astrocytes. To substantiate this hypothesis, we compared the distribution of 2, GLAST and/or GLT-1 in the rat cerebral cortex using double immunofluorescence and confocal microscopy, and immunocytochemistry at the electron microscopic level. We also investigated the relationship between 2, GLAST or GLT-1 and asymmetrical synaptic junctions (largely glutamatergic) and GABAergic nerve terminals. Results show that the 2 subunit has an exclusive astroglial localization, and that it is almost completely co-distributed with GLAST and GLT-1 when evaluated by confocal microscopy. This similar distribution was confirmed at the ultrastructural level, which further showed that the vast majority of the 2 staining (73% of all labelled elements), like that of GLAST and GLT-1, was located in glial leaflets surrounding dendritic spines and the dendritic and/or axonal elements of asymmetrical (glutamatergic) axo-dendritic synapses. Synapses ensheathed by 2, GLAST or GLT-1 virtually never included (
2%) GABAergic nerve terminals or synaptic junctions. However, a subset of GABAergic nerve terminals (10–14%) were directly apposed to asymmetrical axo-dendritic junctions surrounded by 2, GLAST or GLT-1. Altogether these results demonstrate that 2, GLAST and GLT-1 have comparable perisynaptic distribution within cortical astrocytes most likely associated with glutamatergic synapses.
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