Glutamate transporters in glial plasma membranes: Highly differentiated localizations revealed by quantitative ultrastructural immunocytochemistry

Abstract

The glutamate transporters GLT-1 and GLAST were studied by immunogold labeling on ultrathin sections of rat brain tissue embedded in acrylic resins at low temperature after freeze substitution. Both proteins were selective markers of astrocytic plasma membranes. GLT-1 was much higher in hippocampal astrocytes than in cerebellar astrocytes. Astroglial membrane GLAST densities ranked as follows: Bergmann > cerebellar granular layer approximately hippocampus > cerebellar white matter. No astrocyte appeared unlabeled. Astrocytic membranes facing capillaries, pia, or stem dendrites were lower in glutamate transporters than those facing nerve terminals, axons, and spines. Parallel fiber boutons (glutamatergic) synapsin on interneuron dendritic shafts were surrounded by lower transporter densities than those synapsing on Purkinje cell spines. Our findings suggest the localizations of glutamate transporters are carefully regulated.

Striatal Excitatory Amino Acid Transporter Transcript Expression in Schizophrenia, Bipolar Disorder, and Major Depressive Disorder

“…Because EAAT3 and EAAT4 are expressed in neurons whereas EAAT1 and EAAT2 are expressed in astroglia, our results suggest an abnormality associated with neurons, but not astroglia, in the glutamate synapse (Bar-Peled et al 1997;Chaudhry et al 1995;Furuta et al 1997;Milton et al 1997;Rothstein et al 1994;Yamada et al 1996Yamada et al , 1997. Interestingly, we have previously reported abnormalities in EAAT1 and EAAT2, but not EAAT3 or EAAT4, mRNA expression in the thalamus, a finding consistent with the notion of localization of glutamatergic abnormalities within the synapse to specific cell types in given brain regions .…”

“…The transporters have specific patterns of cellular localization: EAAT1 and EAAT2 have been localized to astroglia, whereas EAAT3 and EAAT4 are localized to neurons (Bar-Peled et al 1997;Chaudhry et al 1995;Furuta et al 1997;Lehre et al 1995;Milton et al 1997;Rothstein et al 1994;Sims and Robinson 1999;Yamada et al 1996Yamada et al , 1997. The best studied of the glutamate transporters, EAAT2 (called GLT-1 in the rat) accounts for ‫ف‬ 90% of forebrain glutamate reuptake in the rodent (Rothstein et al 1996;Tanaka et al 1997).…”

Valproic acid inhibits histone deacetylase activity and suppresses excitotoxicity-induced GAPDH nuclear accumulation and apoptotic death in neurons

“…23 The role of EAATs in SYM-induced apoptosis is further supported by the observations that EAAT inhibitors exacerbate endogenous glutamate-induced excitotoxicity through NMDA receptor activation, 24 and that SYM is one of the most potent inhibitors of EAATs, 14 which are expressed in CGC neurons. 25,26 Our pioneering studies show that GAPDH overexpression and nuclear translocation is involved in apoptosis of several cell types subjected to various insults. 16,[18][19][20]27 This role of GAPDH in apoptosis is supported by these studies, which demonstrate that GAPDH antisense oligonucleotides suppress GAPDH overexpression and nuclear translocation and protect cells from apoptotic insults.…”

Morphological plasticity of astroglia: Understanding synaptic microenvironment

“…For example, Bergmann glia in the cerebellum exhibit high levels of GLAST (EAAT1) and almost no GLT‐1 (EAAT2). In contrast, astrocytes in the hippocampus have very high levels of GLT‐1 and hardly any GLAST (Chaudhry et al, 1995; Furuta et al, 1997; Tzingounis and Wadiche, 2007). Furthermore, expression of glutamate transporters seems to depend on neuronal activity: decreased synaptic activity appears to downregulate levels (Benediktsson et al, 2012; Yang et al, 2009).…”