| Abstract No.: | C-B3049 |
| Country: | Canada |
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| Title: | DISTINCT TEMPORAL RECRUITMENT OF HIPPOCAMPAL TYPE III INTERNEURON-SPECIFIC INTERNEURONS BY DIFFERENT EXCITATORY AFFERENTS |
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| Authors/Affiliations: | 1 Lisa Topolnik*;
1 Université Laval, Québec, QC, Canada
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| Content: | Objectives: The activity of GABAergic inhibitory interneurons appears to be tightly organized in space and time through specific patterns of inhibition provided by other local circuit interneurons. These interneuron-specific interneurons (ISIs), specialized to innervate exclusively GABAergic cells, can be divided into three types with distinct morphology and connectivity. The specific role of ISIs in the regulation of their GABAergic targets and the local circuit dialogue remain undetermined.
Materials and methods: I performed whole-cell current- and voltage-clamp recordings of type III ISIs (ISIs-III) in acute hippocampal slices of wild type and GAD67-GFP mice. Excitatory postsynaptic currents (EPSCs) were evoked in ISIs-III by minimal stimulation of the Schaffer collaterals and the perforant path. The type III ISI affiliation of recorded neurons was ascertained by post-hoc morphological and neurochemical (immunodetection of vasoactive intestinal polypeptide) analysis.
Results: ISIs-III demonstrated relatively hyperpolarized resting membrane potential, fast membrane time constant and the regular-spiking firing pattern. EPSCs evoked in ISIs-III by the stimulation of Schaffer collaterals were significantly larger and faster than those evoked by the stimulation of perforant path. To determine the temporal pattern of activity at these two synapses, I next compared the properties of short-term plasticity of EPSCs between the two excitatory inputs. Schaffer collateral–mediated EPSCs demonstrated short-term depression whereas the perforant path–evoked EPSCs showed short-term facilitation. Furthermore, Schaffer collateral–EPSCs were not affected by the NMDA receptor antagonist but were highly sensitive to the Ca2+ permeable AMPA receptor blocker. In contrast, perforant path–EPSCs revealed a significant component mediated by the NMDA in addition to AMPA receptors.
Conclusion: The results of this study demonstrate that synapses formed onto ISIs-III by different excitatory afferents possess specific kinetics and filtering properties as well as distinct postsynaptic receptor composition. These synapse-specific mechanisms of input integration suggest that the two major excitatory pathways converging onto ISIs-III are likely to provide temporally distinct excitation and, accordingly, recruitment of this type of interneurons during ongoing hippocampal activity.
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