| dc.description.abstracteng | Although they represent only a small portion of cortical neurons, inhibitory interneurons take a major role in controlling the activity of cortical excitatory cells and, hence, cortical processing. The interaction of cortical inhibitory neurons, especially in the form of disinhibitory circuits, is the recent subject of scientific investigations. Disinhibition of cortical excitatory cells, for example, gates information flow through cortical columns. One of the key players in inhibiting excitatory neurons are Martinotti cells (MC). This specific cell type is known to receive inhibitory input and thus could be a main relay cell for disinhibitory connections affecting cortical pyramidal cells.
By means of glutamate uncaging we found that MCs in layer II/III of the primary somatosensory cortex receive inhibitory input from local sources, whereas layer V MCs receive local as well as interlaminar inhibitory input. Paired recordings revealed that the local inhibitory input of MCs in layer II/III and V is provided by parvalbumin-expressing (PV-) and vasoactive intestinal polypeptide expressing (VIP-) cells. Furthermore, layer V MCs receive interlaminar inhibitory input from layer II/III. PV-cells caused stronger synaptic input in layer II/III MCs as compared to VIP-cells. Additionally, these two unitary connections showed significant differences in elementary synaptic properties. Moreover, PV-cell input showed frequency-independent depression whereas VIP-cell input facilitated at high frequencies. This local connectivity scheme is also present in layer V of the primary somatosensory cortex. There, PV-cells cause inhibitory input onto MCs with a similar strength and short-term synaptic plasticity. Although the local VIP to MC connection seems to be present as well in L V, further experiments are necessary to firmly establish this connectivity in terms of probability and effect. Furthermore, VIP-cells in layer II/III are likely the source of interlaminar inhibitory input of layer V MCs. In conclusion, the observed differences in the properties of the two unitary connections enable disinhibition of pyramidal cells (PC) with opposed spatial and temporal features. Viewed spatially, PV-cells might control spiking output of MCs, whereas VIP-cells might be able to control excitatory inputs to MCs. Furthermore, PV-cells may induce a transient release from MC inhibition, whereas VIP-cells may result in tonic disinhibition of PCs via MCs. | de |