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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.