Differential distribution of the glutamate transporters GLT1 and rEAAC1 in rat cerebral cortex and thalamus: an in situ hybridization analysis

Abstract

The distributions in rat cerebral cortex and thalamus of the mRNAs encoding the glutamate transporters GLT1 and rEAAC1 (a rat homologue of rabbit EAAC1) were investigated by nonautoradiographic in situ hybridization using digoxigenin-labelled riboprobes. The probe recognizing rEAAC1 mRNA labelled exclusively neurons while GLT1 mRNA was found in glia as well as in select neuronal populations. The neurons containing the GLT1 transcript exhibited a distribution that was different from, and at some sites complementary to, the distribution of neurons containing rEAAC1 mRNA. In the subiculum, neurons positive for GLT1 and rEAAC1 were found in the deep and superficial part of the cell layer, respectively, while in the parietal neocortex GLT1 predominated in layer VI and rEAAC1 in layer V. Very few neuronal populations, most notably cells in hippocampal subfields CA3 and CA4, and in layer II in the entorhinal cortex, appeared to be equipped with both transcripts. In the thalamus 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, laminar, as well as regional heterogeneities in the expression of the two glutamate transporters.

The Density of EAAC1 (EAAT3) Glutamate Transporters Expressed by Neurons in the Mammalian CNS

“…This is in agreement with many (Kanai and Hediger, 1992;Rothstein et al, 1994;Coco et al, 1997;Shashidharan et al, 1997;Torp et al, 1997;Berger and Hediger, 1998;Plachez et al, 2000;Holmseth et al, 2005), but not all (Conti et al, 1998;Kugler and Schmitt, 1999) previous immunocytochemical studies. The apparent immunolabeling of non-neuronal cells may, in part, be explained by the tendency of a part of the EAAC1 sequence (IVNPFALEPTILDNEDSDTK) to induce generation of antibodies that cross-react with tubulin (Holmseth et al, 2005).…”

The Glutamate Transporter GLT1a Is Expressed in Excitatory Axon Terminals of Mature Hippocampal Neurons

“…The identification of GLT1 as a presynaptic transporter is fully compatible with the available evidence, exhaustively reviewed by Danbolt (2001): the presence of transcripts for GLT1 in neurons throughout the forebrain (Schmitt et al, 1996;Torp et al, 1997;Berger and Hediger, 1998); the demonstration of glutamate uptake into cortical synaptosomes (Beart, 1976) that is inhibited by dihydrokainate (Ferkany and Coyle, 1986;Robinson et al, 1993;Koch et al, 1999;Suchak et al, 2003), which, at low concentrations (Ͻ300 M), is an inhibitor exclusively of GLT1 among the known transporters (Arriza et al, 1994;Tan et al, 1999;Chen et al, 2002;Kalandadze et al, 2002); the expression of GLT1 in neurons in vitro (Mennerick et al, 1998;Wang et al, 1998;Chen et al, 2002); and the increase in cross-talk between neighboring synapses by dihydrokainate (Asztely et al, 1997;Bergles and Jahr, 1998). The simplest explanation for these observations is that presynaptic uptake of glutamate is, in fact, mediated by the expression of GLT1, at least in some excitatory terminals.…”

“…GLT1 mRNA has been found by several groups to be expressed in neurons in the mature brain, most prominently in the CA3 region of the hippocampus (Schmitt et al, 1996;Torp et al, 1997;Berger and Hediger, 1998), but without associated expression of the protein (Danbolt, 2001). The motivation for the present study was to retest the hypothesis that GLT1 occurs in neurons and to determine whether the dominant form is GLT1a or GLT1b.…”

The identification of vesicular glutamate transporter 3 suggests novel modes of signaling by glutamate

“…Although we observed expression of VGLUT3 mRNA by hippocampal pyramidal and dentate gyrus granule cells, we did not detect VGLUT3 protein at their terminals. These neurons have been observed to express mRNAs without the corresponding proteins (30).…”