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Fast Micro-iontophoresis of Glutamate and GABA: A Useful Tool to Investigate Synaptic Integration
Published on: July 31, 2013
Extrasynaptic glutamate receptor activation as cellular bases for dynamic range compression in pyramidal neurons
Katerina D Oikonomou1, Shaina M Short, Matthew T Rich
1Department of Neuroscience, University of Connecticut Health Center Farmington, CT, USA.
Frontiers in Physiology
|August 31, 2012
Summary
Excess extracellular glutamate activates extrasynaptic NMDA receptors, generating dendritic plateau potentials. These potentials exhibit properties similar to cortical UP states and contribute to signal compression in pyramidal neurons.
Area of Science:
- Neuroscience
- Cellular Biology
- Computational Neuroscience
Background:
- Astrocytic glutamate uptake is crucial for regulating extracellular glutamate levels.
- Repetitive neuronal activity can overwhelm astrocytic clearance, leading to transient glutamate accumulation.
- Extrasynaptic NMDA receptors play a role in neuronal excitability and plasticity.
Purpose of the Study:
- To investigate the functional consequences of extrasynaptic NMDA receptor activation during periods of high extracellular glutamate.
- To characterize the dendritic events triggered by sustained glutamate exposure.
- To elucidate the role of these events in neuronal signal processing and dynamic range compression.
Main Methods:
- Utilized voltage-sensitive and calcium-sensitive dyes to monitor dendritic activity in pyramidal neurons.
- Induced excess extracellular glutamate via repetitive synaptic stimulation or iontophoresis.
- Recorded neuronal responses to varying patterns of synaptic input.
Main Results:
- Repetitive stimulation led to dendritic plateau potentials, distinct from NMDA spikes, with widespread calcium influx.
- These plateau potentials, initiated by extrasynaptic NMDA receptor activation, were sustained and resistant to interruption.
- Dendritic plateau potentials were summed sublinearly at the soma, demonstrating signal compression.
Conclusions:
- Sustained depolarization and plateau potentials depend on glutamate surplus near extrasynaptic receptors.
- Extrasynaptic NMDA receptors enable dynamic range compression in pyramidal neurons, akin to audio engineering.
- This mechanism explains the uniform amplitude of consecutive cortical UP states.
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