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Karri Lamsa"Pathway-specific LTP in hippocampal feed-forward inhibitory interneurons"

Abstract :

LTP in feed forward inhibitory interneurons preserves fidelity of temporal discrimination in the hippocampus

Cortical feed-forward interneurons play a central role in ensuring precise temporal discrimination among excitatory inputs to principal neurons: because GABAergic inhibition lags behind monosynaptic glutamatergic excitation, the integration window for postsynaptic action potential generation is restricted to a very narrow interval. How is temporal coincidence detection maintained in the face of synaptic plasticity that underlies memory encoding? Although glutamatergic transmission to pyramidal neurons exhibits robust pathway-specific NMDA receptor-dependent long-term potentiation (LTP), there is scanty evidence that this phenomenon also occurs in inhibitory interneurons. If glutamatergic transmission to interneurons is relatively unvarying, this leads to the prediction that learning-related plasticity of transmission to principal cells should be accompanied by a degradation of temporal precision of information processing.

We demonstrate Hebbian (pathway-specific, NMDA receptor-dependent) LTP in a population of hippocampal feed-forward inhibitory interneurons. We further show that Hebbian LTP in interneurons propagates to pyramidal neurons. Finally, we show that, although temporal discrimination is, indeed, compromised when LTP is restricted to synapses on pyramidal neurons, it is restored when LTP is also allowed to occur at synapses on interneurons.

LTP at synapses on feed-forward interneurons thus preserves the fidelity of temporal discrimination in the face of learning-associated plasticity. 

Christophe Mulle