EXPRESSION OF THE GLUTAMATE TRANSPORTER GLT1 IN NEURAL CELLS OF THE RAT CENTRAL-NERVOUS-SYSTEM - NONRADIOACTIVE IN-SITU HYBRIDIZATION AND COMPARATIVE IMMUNOCYTOCHEMISTRY

Non-radioactive in situ hybridization using complementary RNA and olig onucleotide probes was applied in order to clearly identify the cell t ypes expressing GLT1 and to show their regional distribution in the ce ntral nervous system of the rat. The results were compared with immuno cytochemical data achieved using an antibody against a synthetic GLT1 peptide. The study showed that GLT1 was expressed in astrocytes and Be rgmann glia which were identified by the detection of an astrocytic ma rker protein. Additionally, subsets of neurons in different brain regi ons (e.g., CA3/4 pyramidal cells of the hippocampus, endopiriform nucl eus) were labelled by in situ hybridization. In other cell types of th e central nervous system (oligodendrocytes, ependymal cells, epithelia l cells of the choroid plexus, tanycytes), GLT1 expression was not det ectable. The generally dense astrocytic immunolabelling of the gray ma tter of the brain showed an even higher intensity in regions reported to show high glutamatergic activity and astrocytic glutamate metabolis m (e.g., the termination field of the glutamatergic perforant path in the hippocampus). On the basis of the cellular regional distribution o f 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 le vels.