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GABA transporters in the mammalian cerebral cortex: localization, development and pathological implications.
No full textThe extracellular levels of GABA, the main inhibitory neurotransmitter in the mammalian cerebral cortex, are regulated by specific high-affinity, Na+/Cl--dependent transporters. Four distinct genes encoding GABA transporters (GATs), named GAT-1, GAT-2, GAT-3, and BGT-1 have been identified using molecular cloning Of these, GAT-1 and -3 are expressed in the cerebral cortex. Studies of the cortical distribution, cellular localization, ontogeny and relationships of GATs with GABA-releasing elements using a variety of light and electron microscopic immunocytochemical techniques have shown that: i) a fraction of GATs is strategically placed to mediate GABA uptake at fast inhibitory synapses, terminating GABA’s action and shaping inhibitory postsynaptic responses; ii) another fraction may participate in functions such as the regulation of GABA’s diffusion to neighboring synapses and of GABA levels in cerebrospinal fluid; iii) GATs may play a role in the complex processes regulating cortical maturation; iv) GATs may contribute to the dysregulation of neuronal excitability that accompanies at least two major human diseases: epilepsy and ischemia
Clozapine-induced reduction of glutamate transport in the frontal cortex is not mediated by GLAST and EAAC1
No full textPlasma membrane transporters GAT-1 and GAT-3 contribute to heterogeneity of GABAergic synapses in neocortex.
Full text linkA Reappraisal of GAT-1 Localization in Neocortex
Full text linkγ-Aminobutyric acid (GABA) transporter (GAT)-1, the major GABA transporter in the brain, plays a key role in modulating GABA signaling and is involved in the pathophysiology of several neuropsychiatric diseases, including epilepsy. The original description of GAT-1 as a neuronal transporter has guided the interpretation of the findings of all physiological, pharmacological, genetic, or clinical studies. However, evidence published in the past few years, some of which is briefly reviewed herein, does not seem to be consistent with a neurocentric view of GAT-1 function and calls for more detailed analysis of its localization. We therefore performed a thorough systematic assessment of GAT-1 localization in neocortex and subcortical white matter. In line with earlier work, we found that GAT-1 was robustly expressed in axon terminals forming symmetric synapses and in astrocytic processes, whereas its astrocytic expression was more diffuse than expected and, even more surprisingly, immature and mature oligodendrocytes and microglial cells also expressed the transporter. These data indicate that the era of “neuronal” and “glial” GABA transporters has finally come to a close and provide a wider perspective from which to view GABA-mediated physiological phenomena. In addition, given the well-known involvement of astrocytes, oligodendrocytes, and microglial cells in physiological as well as pathological conditions, the demonstration of functional GAT-1 in these cells is expected to provide greater insight into the phenomena occurring in the diseased brain as well as to prompt a reassessment of earlier findings
A quantitative analysis of cellular and synaptic localization of GAT-1 and GAT-3 in rat neocortex
No full textLight microscopic identification and immunocytochemical characterization of glutamatergic synapses in brain sections.
No full textABSTRACT
Presynaptic proteins are readily identified by light microscopic immunocytochemistry, but
immunodetection of postsynaptic proteins in brain sections proves difficult. We performed immunofluorescent
double labeling for the NR1 subunit of the N-methyl-D-aspartate receptor
(NMDAR) and the vesicular glutamate transporter 1 (VGLUT1). In material fixed with 4%
paraformaldehyde, NMDAR staining in somatosensory cortex was restricted to the section
surface, whereas presynaptic staining extended deeper into the tissue. Staining for postsynaptic
proteins was enhanced in weakly fixed material and in tissue treated with pepsin, as previously
reported, but tissue quality was impaired. Staining was also markedly enhanced, and without
impairment of tissue quality, by treatment during perfusion with a mixture of inhibitors of
proteases and the ubiquitin/proteosome system. We performed quantitative analysis of confocal
images to study how immunostaining varies with depth into the tissue. Virtually all puncta
immunopositive for VGLUT1 colocalized with synaptophysin puncta; these presynaptic puncta
were most numerous 1–2 mbeneath the section surface. In contrast, puncta immunopositive for
the NR1 subunit were most numerous at the surface, as were puncta immunopositive for the NR2
subunit, SynGAP, and CaMKII. Punctate staining for all postsynaptic proteins, but not presynaptic
markers, was substantially enhanced in material pretreated with antiproteolytic agents.
The large majority of NR1-positive puncta at the surface associated with VGLUT1 in this
material are likely to represent synaptic contacts. Approximately eighty-five percent of VGLUT1-
positive puncta in layers II–III of SI are associated with NR1-positive puncta, and 80% are
associated with NR2, SynGAP, and CaMKII. This approach may permit systematic analysis of
the chemistry of glutamatergic synapses with light microscopic immunocytochemistry
Localization of the Na(+)-coupled neutral amino acid transporter 2 in the cerebral cortex.
No full textIncreased expression of the astrocytic glutamate transporter GLT-1 in the prefrontal cortex of schizophrenics
No full textMELONE M. and MATUTE C.: co-first author
ABSTRACT
To verify whether altered glial glutamate uptake contributes to the
reduced efficacy of glutamatergic transmission reported in the prefrontal cortex of
schizophrenics, we studied the expression of GLT-1, the transporter responsible for most
glutamate transport, in autoptic samples of prefrontal cortex using real time quantitative
RT-PCR, immunocytochemistry, and functional assays. GLT-1 mRNA levels in
medication-free patients were 2.5-fold higher than in controls, whereas they were
normal or reduced in patients treated with antipsychotics. We also observed a 4-fold
increase in L-[3H]-Glu uptake in Xenopus oocytes injected with mRNA from the prefrontal
cortex of a medication-free schizophrenic and a 2-fold increase in GLT-1 protein in
the same cortical area of another medication-free patient. Results suggest that GLT-1
mRNA, protein and function are increased in prefrontal cortex of schizophrenics
GLT-1 up-regulation enhances the effect of PCP on prepulse inhibition of the startle reflex in adult rats.
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