Extracellular Glutamate in the Nucleus Accumbens Is Nanomolar in Both Synaptic and Non-synaptic Compartments

Publication date: 14 March 2017
Source:Cell Reports, Volume 18, Issue 11
Author(s): Delia N. Chiu, Craig E. Jahr
In the CNS, glutamate is both phasically and tonically released into the extracellular space and must be removed by excitatory amino acid transporters (EAATs) to prevent excitotoxic accumulation. There remains uncertainty, however, regarding the functional steady-state concentration, with estimates ranging from tens of nanomolar to tens of micromolar. Efforts to reconcile these disparate values have led to a hypothesis that the extracellular space comprises distinct compartments in which basal glutamate concentrations are maintained independently. We used electrophysiology and two-photon Ca²⁺ imaging to test this hypothesis in the nucleus accumbens (NAc), where it has been proposed that micromolar extracellular glutamate is necessary for normal function. We found that the average concentration of synaptic glutamate is nanomolar, in agreement with previous electrophysiological estimates. Furthermore, this held true when glutamate uptake was inhibited, indicating that extracellular glutamate is not compartmentalized by EAATs.

Graphical abstract

Teaser

Glutamate is present in the extracellular space surrounding neurons, but it is unclear whether the steady-state concentration in synaptic and non-synaptic areas is the same. Chiu and Jahr show that basal extracellular glutamate is nanomolar, both inside and outside the synaptic cleft.


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