DIFFERENTIAL DISTRIBUTION OF THE GLUTAMATE TRANSPORTERS GLT1 AND REAAC1 IN RAT CEREBRAL-CORTEX AND THALAMUS - AN IN-SITU HYBRIDIZATION ANALYSIS

The distributions in rat cerebral cortex and thalamus of the mRNAs enc oding the glutamate transporters GLT1 and rEAAC1 (a rat homologue of r abbit EAAC1) were investigated by nonautoradiographic in situ hybridiz ation using digoxigenin-labelled riboprobes. The probe recognizing rEA AC1 mRNA labelled exclusively neurons while GLT1 mRNA was found in gli a as well as in select neuronal populations. The neurons containing th e GLT1 transcript exhibited a distribution that was different from, an d at some sites complementary to, the distribution of neurons containi ng rEAAC1 mRNA. In the subiculum, neurons positive for GLT1 and rEAAC1 were found in the deep and superficial part of the cell layer, respec tively, while in the parietal neocortex GLT1 predominated in layer VI and rEAAC1 in layer V. Very few neuronal populations, most notably cel ls in hippocampal subfields CA3 and CA4, and in layer II in the entorh inal cortex, appeared to be equipped with both transcripts. In the tha lamus the GLT1 labelling predominated in the midline and intralaminar nuclei while rEAAC1 labelling was found throughout this structure. It was concluded that the cerebral cortex and thalamus show cellular, lam inar, as well as regional heterogeneities in the expression of the two glutamate transporters.