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Updated: Jul 12, 2026
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Horizontal Hippocampal Slices of the Mouse Brain
Published on: September 22, 2020
Extracellular glutamate concentration in hippocampal slice
Melissa A Herman1, Craig E Jahr
1Vollum Institute, Oregon Health and Science University, Portland, Oregon 97239, USA.
Summary
Extracellular glutamate concentrations are much lower than previously thought, near 25 nM. This nanomolar range is too low to significantly activate neuronal receptors like NMDA receptors (NMDARs).
Area of Science:
- Neuroscience
- Neurochemistry
Background:
- Extracellular glutamate exists at low baseline concentrations, with previous estimates up to 4 microM.
- High baseline glutamate could activate or desensitize receptors, affecting neuronal excitability.
Purpose of the Study:
- To accurately measure extracellular glutamate baseline concentrations in the hippocampus.
- To determine the functional impact of previously reported versus measured glutamate levels on neuronal activity.
Main Methods:
- Utilized NMDA receptors (NMDARs) in CA1 pyramidal cells of acute hippocampal slices to monitor extracellular glutamate.
- Superfused slices with varying glutamate and NMDA concentrations to assess receptor activation and transport effects.
Main Results:
- Measured hippocampal extracellular glutamate baseline concentration near 25 nM, significantly lower than prior estimates.
- Superfusion with micromolar glutamate did not affect neurons, indicating effective glutamate transport.
- NMDA, a non-transported agonist, caused significant neuronal depolarization at equipotent concentrations.
Conclusions:
- Ambient extracellular glutamate concentrations in the hippocampus are in the nanomolar range.
- These low concentrations are insufficient to cause significant activation of glutamate receptors in vivo.
- Glutamate transport mechanisms effectively limit receptor access to extracellular glutamate.
