Expression of the glutamate transporter GLT1 in neural cells of the rat central nervous system: Non-radioactive in situ hybridization and comparative immunocytochemistry

Non-radioactive in situ hybridization using complementary RNA and oligonucleotide probes was applied in order to clearly identify the cell types expressing GLT1 and to show their regional distribution in the central nervous system of the rat. The results were compared with immunocytochemical data achieved using an antibody against a synthetic GLT1 peptide. The study showed that GLT1 was expressed in astrocytes and Bergmann glia which were identified by the detection of an astrocytic marker protein. Additionally, subsets of neurons in different brain regions (e.g., CA3/4 pyramidal cells of the hippocampus, endopiriform nucleus) were labelled by in situ hybridization. In other cell types of the central nervous system (oligodendrocytes, ependymal cells, epithelial cells of the choroid plexus, tanycytes), GLT1 expression was not detectable. The generally dense astrocytic immunolabelling of the gray matter of the brain showed an even higher intensity in regions reported to show high glutamatergic activity and astrocytic glutamate metabolism (e.g., the termination field of the glutamatergic perforant path in the hippocampus). On the basis of the cellular regional distribution of the GLT1 messenger RNA and protein demonstrated in the present study, it is reasonable to assume that this high affinity transporter is of importance for the maintenance of adequate extraneuronal glutamate levels.