Differential expression of two glial glutamate transporters in the rat brain: quantitative and immunocytochemical observations

Abstract

Glutamate, the major excitatory neurotransmitter in brain, is almost exclusively intracellular due to the action of the glutamate transporters in the plasma membranes. To study the localization and properties of these proteins, we have raised antibodies specifically recognizing parts of the sequences of two cloned rat glutamate transporters, GLT-1 (Pines et al., 1992) and GLAST (Storck et al., 1992). On immunoblots the antibodies against GLT-1 label a broad heterogeneous band with maximum density at around 73 kDa, while the antibody against GLAST labels a similarly broad band at around 66 kDa in the cerebellum and a few kilodaltons lower in other brain regions. GLT-1 is expressed at the highest concentrations in the hippocampus, lateral septum, cerebral cortex, and striatum, while GLAST is preferentially expressed in the molecular layer of the cerebellum. However, both transporters are present throughout the brain, and have roughly parallel distributions in the cerebral hemispheres and brainstem. Preembedding light and electron microscopical immunocytochemistry shows that both GLT-1 and GLAST are restricted to astrocytes, which appear to express both proteins concomitantly, but in different proportions in different parts of the brain. Nerve terminal labeling was not observed. Both the amino and carboxyl terminals of GLT- 1 and GLAST are located intracellularly, indicating an even number of transmembrane segments. Antibodies against a synthetic peptide corresponding to amino acid residues 2–11 of the proposed sequence of GLT-1 recognize the native rat brain GLT-1 protein, confirming that the translation initiation site is at the first ATG.

Functional Expression of a GLT‐1 Type Na+‐Dependent Glutamate Transporter in Rat Pinealocytes

“…In the present study, we show that a GLT-1-type Nat-dependent transporter functions in rat pinealocytes. Because GLT-l is known to be localized only in astrocytes Rothstein et al, 1994;Lehre et al, 1995), this is the first observation of the presence of a GLT-1-like transporter in endocrine cells.…”

Blockade of the GLT-1 Transporter in the Central Nucleus of the Amygdala Induces both Anxiety and Depressive-Like Symptoms

“…Similarly, downregulation in the high-affinity astrocytic glutamate transporters SLC1A2 (EAAT2) and SLC1A3 (EAAT1) has been identified in the anterior cingulate of postmortem human tissue (Choudary et al, 2005); abnormalities that may contribute to elevated glutamate levels in the amygdala because of dense connectivity between the two regions (Carmichael and Price, 1995;Ongur and Price, 2000). These findings suggest compromised metabolism of glutamate in the depressed brain, and as astrocytes account for at least 90 percent of glutamate uptake (Chaudhry et al, 1995;Lehre et al, 1995;Haugeto et al, 1996;Lehre and Danbolt, 1998), deficits in glial cells may drive the increased cortical activation reported in depression. These findings suggest that heightened activity in the amygdala may contribute to increased anxiety in depressed patients.…”

Macrophages and HIV-1: dangerous liaisons

“…These effectors are not expressed in normal brains (Lehre et al, 1995), and are highly dependent on cell activation and differentiation in vitro (Rimaniol et al, 2000). This strongly suggests a compensatory mechanism that responds to depressed astrocytic function.…”