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GABA-activated Single-channel and Tonic Currents in Rat Brain Slices
Published on: July 17, 2011
Unitary inhibitory field potentials in the CA3 region of rat hippocampus
Michaël Bazelot1, Céline Dinocourt, Ivan Cohen
1INSERMU975, CHU Pitié-Salpêtrière, 105 bd de l'Hôpital, Paris, France.
Insights
Single hippocampal interneurons generate field potentials at monosynaptic latencies. These inhibitory fields, originating from distinct axonal arborizations, were detected across the CA3 region.
Area of Science:
- Neuroscience
- Electrophysiology
- Cellular Biology
Background:
- Previous research suggested single hippocampal interneurons evoke field potentials at monosynaptic latencies.
- The precise origin and propagation of these field potentials require further investigation.
Purpose of the Study:
- To investigate the origin and characteristics of field potentials generated by single hippocampal interneurons.
- To differentiate between interneuron- and pyramidal cell-initiated field potentials.
- To analyze the spatial distribution and kinetics of inhibitory field potentials.
Main Methods:
- Simultaneous intracellular and multiple extracellular recordings from rat hippocampal CA3 slices.
- GABAergic nature confirmation via low external chloride concentration.
- Extracellular electrode arrays and cluster analysis for spatial distribution and event separation.
Main Results:
- Interneurons evoke field potentials at monosynaptic latencies.
- Pyramidal cells initiate disynaptic inhibitory fields, not detectable monosynaptic excitatory fields.
- Inhibitory fields are GABAergic and postsynaptic, suppressed by low external chloride.
- Single interneuron-evoked fields detected over >800 µm along stratum pyramidale.
- Dendritic vs. perisomatic inhibitory events show differences in frequency and kinetics.
- Distinct axonal arborizations of interneurons distinguished by field potential initiation.
Conclusions:
- Single hippocampal interneurons are primary generators of monosynaptic field potentials.
- Inhibitory field potentials exhibit spatial and temporal heterogeneity based on interneuron connectivity.
- This study provides detailed insights into the cellular origins of hippocampal network activity.
Abstract:
Glickfeld and colleagues (2009) suggested that single hippocampal interneurones generate field potentials at monosynaptic latencies. We pursued this observation in simultaneous intracellular and multiple extracellular records from the CA3 region of rat hippocampal slices. We confirmed that interneurones evoked field potentials at monosynaptic latencies. Pyramidal cells initiated disynaptic inhibitory field potentials, but did not initiate detectable monosynaptic excitatory fields. We confirmed that inhibitory fields were GABAergic in nature and showed they were suppressed at low external Cl(-), suggesting they originate at postsynaptic sites. Field potentials generated by a single interneuron were detected at multiple sites over distances of more than 800 mum along the stratum pyramidale of the CA3 region. We used arrays of extracellular electrodes to examine amplitude distributions of spontaneous inhibitory fields recorded at sites orthogonal to or along the CA3 stratum pyramidale. Cluster analysis of spatially distributed inhibitory field events let us separate events generated by interneurones terminating on distinct zones of somato-dendritic axis. Events generated at dendritic sites had similar amplitudes but occurred less frequently and had somewhat slower kinetics than perisomatic events generated near the stratum pyramidale. In records from multiple sites in the CA3 stratum pyramidale, we distinguished inhibitory fields that seemed to be initiated by interneurones with spatially distinct axonal arborisations.
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