In current clamp, the same neurons reached an average maximal depolarization at 450 m (calculated in in the final 100 ms of the photo-stimulus) of 7??5 mV (n?=?7), which was rarely enough to drive spiking on its own. Gamma oscillations generated in separate cortical locations exhibited high coherence as far apart as 850 m, and lateral gamma entrainment depended on SOM neuron activity. These data identify a circuit that is sufficient to mediate long-range gamma-band coherence in Monensin sodium the primary visual cortex. electroporation (Saito and Nakatsuji, 2001), and a slow ramp of blue light targeted to L2/3 was used to reliably drive oscillatory network activity. Under these conditions, ChR2 expression is restricted to excitatory neurons (Figure 1figure supplement 1) (Adesnik and Scanziani, 2010), and therefore all optogenetically evoked inhibition is driven polysynaptically through the network, rather than being of monosynaptic origin. Consistent with prior work in both S1 and V1, wide-field illumination of L2/3 generates strong gamma rhythms in excitatory and inhibitory currents measured in L2/3 cortical neurons (Figure 1A,B). To gain control over the spatial profile of excitation, we built Monensin sodium and characterized a digital-micromirror-device (DMD) based illumination system that generates arbitrary multicolor light patterns with high spatial and temporal precision (Figure 1figure supplement 2, Figure 4figure supplement 1). Using this system, we found that the power of the gamma oscillations depended on the area of illumination, reminiscent of the dependence of gamma oscillations on visual stimulus size in vivo (Gieselmann and Thiele, 2008; Jia et al., 2013; Ray et al., 2013; Veit et al., 2017) (Figure 1C. Analyzed from 0 to 1000 ms post-stimulus onset.). Open in a separate window Figure 1. Horizontal circuits recruit local SOM interneurons to synchronize distant gamma generators.(A) Experimental schematic: A ChR2-negative Pyramidal Rabbit Polyclonal to ATG4D cell is recorded in L2/3 of V1 while other ChR2-expressing L2/3 neurons are photo-stimulated with different sizes of blue light stimuli using a digital-micromirror-device (DMD). (B) Top: Time course of the light stimulus intensity (final intensity 1.1 mW/mm2, see Materials and methods). Bottom: Example traces of voltage-clamped excitatory postsynaptic current (EPSC, red) and inhibitory postsynaptic current (IPSC, blue) during photo-induced gamma rhythms in V1. (C) Plot of peak gamma power versus the width of the photo-stimulus on L2/3 (n?=?8, p<10?4, Kruskal-Wallis ANOVA). Errorbars are s.e.m. (D) Experimental schematic: two ChR2-negative L2/3 pyramidal cells are simultaneously recorded while nearby ChR2-expressing L2/3 PCs are focally activated with separate blue light patches using a digital micro-mirror device (DMD). The distance between the blue light patches ranged from 275 to 850 m (see Figure 1figure supplement 1B). (E) Example traces of the voltage-clamped IPSCs from a pair of simultaneously recorded L2/3 PCs during photo-induction of two separate gamma oscillations. (F) Oscillation-triggered average of the IPSCs recorded in the pair in B) (triggered off the oscillations in one of the two cells, labeled in dark blue). Shading represents one standard deviation. (GCI) As in (DCF) but following a transection of L2/3 between the two recorded L2/3 PCs in transfected slices. (J) Scatter plot of the peak coherence of the oscillations in the two recorded neurons between the cut and the two intact conditions. Mean peak coherence with 275C400 m separation (close): 0.72??0.04, n?=?6 pairs; mean peak coherence at 625C850 m separation (far): 0.44??0.09, n?=?7 pairs; mean peak coherence at 275C400 m with L2/3 cut (cut): 0.11??0.01, n?=?11 pairs; p<10?3, Wilcoxon rank sum test between close and cut conditions; p<10?3, Wilcoxon rank sum test between far and cut conditions. Errorbars are s.e.m. Figure 1figure supplement 1. Open in a separate window electroporation of ChR2-YFP into SOM-Cre, PV-Cre, and wild-type mice and spatial restriction of ChR2 expression to L2/3.(A) Top left: Widefield epifluorescent example image of a 400-m-thick acute slice from a PV-Cre;LSL-tdTomato mouse electroporated with ChR2-YFP at E15.5. Bottom left: Close up confocal image of fixed a 40-m-thick section. Top Right: Widefield epifluorescent example image of a Monensin sodium 400 m thick acute slice from a SOM-Cre;LSL-tdTomato mouse electroporated with ChR2-YFP and GFP at E15.5. Bottom.