Jean-Sébastien Jouhanneau

17 mars 2017

Neural Circuits and Behaviour, Max-Delbrück Center for Molecular Medicine, Helmholtz Association, Berlin, Germany

In vivo monosynaptic transmission within cortical layer 2

invité par Ivo Vanzetta


Abstract Synaptic integration is critical for neocortical sensory processing, cognition and memory formation. However, there is currently no consensus on synaptic integration in vivo mainly due to the lack of experimental data about synaptic integration in vivo. Here we used two-photon microscopy to make visually targeted whole-cell recordings from 2-4 neighbouring identified cortical neurons in the somatosensory cortex of the urethane anaesthetised mouse. We first characterized the synaptic connectivity in vivo looking at kinetics of unitary, excitatory postsynaptic potentials (uEPSPs). Then we investigate the effect of this evoked uEPSP on the dynamic of cortical layer 2 neuronal activity. While single uEPSPs did not affect GABAergic somatostatin-expressing neurons (SSTs) firing rates, it had a pronounced impact on the firing rate of postsynaptic GABAergic parvalbumin-expressing neurons (PVs). On average, postsynaptic PV firing rates increased 3 fold with a strongest case showing a spiking increased from 20 to 200 Hz. PV APs did not track the time course or the integral of uEPSP, but instead were almost completely restricted to the uEPSP rising phase. Moreover, we show that single spike evoked PV firing propagates through the cortical network to inhibit neighboring excitatory neurons, thus providing a circuit for disynaptic inhibition under sparse firing conditions. We conclude that single uEPSPs have a major impact on PV spiking in vivo.

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