The excitatory amino acid carrier 1 (EAAC1) in the rat nucleus of the solitary tract: subcellular localization suggests no major role in glutamate clearance.

Abstract

The excitatory amino acid carrier 1 (EAAC1) is a sodium-dependent glutamate transporter widely found in the mammalian brain and mainly localized in the somatodendritic compartment of neurons. The present study was performed to determine whether EAAC1 is present in the rat nucleus of the solitary tract (NST, a sensory brainstem nucleus involved in visceroception) and to document its subcellular localization. Using fluorescent immunolabeling, peroxidase immunostaining and quantitative immunogold labeling, we showed that both intracellular and plasma membrane-associated pools of EAAC1 transporters existed in dendrites of NST neurons. Although plasma membrane-associated transporters were more concentrated in the vicinity of synapses, no labeling was found at the axon-dendrite interface, suggesting that EAAC1 was not (or barely) expressed in this portion of dendritic membrane. Using computer simulation, we next showed that the ability of EAAC1 to efficiently take up synaptically released glutamate was very low outside the axon-dendrite interface. These data suggest that EAAC1 transporters present on NST dendrites may play a minor role if any in glutamate clearance.