Fig. 2: PrL GABAergic projection neurons preferentially target L1 INs and disinhibit L5 PNs in the Cg1/2.

a Reconstructed pSBC (left) and pNGF (right) responsive to axonal stimulation of GABAergic projections. Somata and dendrites are indicated in black. Axonal arborization is indicated in green and blue. Normalized axonal density for pSBC (n = 6 cells, N = 3 mice) and pNGF (n = 7 cells, N = 3 mice) plotted against horizontal or vertical axes; measurements were performed in 10 μm intervals (black tick indicates location of the soma, horizontal axis: F(160,1760) = 2.673, vertical axis: F(160,1760) = 7.865, ***p < 0.0001, two-way RM ANOVA). Inset, typical firing patterns in response to current injections (−50, near threshold and 50 pA) and corresponding light-evoked IPSCs. Blue columns indicate laser illumination. Note that the light-evoked IPSCs are almost completely abolished (n = 5 cells, N = 3 mice) by the GABA_AR blocker SR95531 (SR, 1 μM). b Summary of IPSC peak amplitude (left; pNGF, n = 16 cells, pSGC, n = 11 cells) and connectivity (right). The number of connections per number of attempts for each cell type is indicated (N = 22 mice). c Experimental setting in a coronal section. Stimulating electrode is placed in L1. GABAergic axon stimulation occurs via blue light. The firing pattern belongs to a pSBC in L1, the approaching recording pipette (rec) is visible on the right. Pial surface is indicated as a dotted line. Inset, the firing patterns of the recorded pSBC. Scale bar, 40 mV, 0.25 s. d Cell-attached recording of the same pSBC shown in (c). Left and right, action currents induced by electrical stimulation (E-stim, triangle) only. Middle, optical stimulation (Opto, blue column) precedes electrical stimulation by 5 ms. e Summary of spiking probability of pSBC (n = 7 cells, N = 4 mice, p = 0.0025) and pNGF (n = 5 cells, N = 3 mice, p = 0.0342) before, during and after optical stimulations. **p < 0.005, *p < 0.05, Friedman test followed by post hoc two-sided Dunn’s test. f Experimental setting for whole-cell recording of L5 PNs. Stimulating electrode is placed in L1, GABAergic axons are activated by blue light. Inset, the firing pattern of a recorded PN. Scale bar, 40 mV, 0.25 s. g, h Electrically evoked responses from the same PN shown in (f). Top, compound PSCs (including EPSC-IPSC sequences and putative pure EPSCs) recorded at −50 mV. Individual traces are superimposed and shown in gray. Averaged traces are shown in black. Two EPSC-IPSC sequences are highlighted in orange. Shaded areas indicate the inward charge. Note that the stimulation not always elicited EPSC-IPSC sequences as the spike probability of L1 INs in (d, e) was always below 100%. Middle, EPSCs recorded at −92 mV (E_GABA). Bottom, feedforward (FF) IPSCs isolated by subtraction (see “Methods”). The onset of the EPSC and of the FF IPSC are indicated in red and black dotted line, respectively. In (h), optical stimulation (blue column) precedes electrical stimulation (triangle) by 5 ms. Stimulation artifacts were removed for clarity sake. i Summary of inward charge recorded at near −50 (blue, n = 12 cells, p = 0.0015) or −92 mV (E_GABA, red, n = 10 cells, p = 0.1055) with and without optical stimulation (N = 4 mice). **p < 0.005, two-sided Wilcoxon signed rank test. j Summary of normalized inward charge recorded at near −50 (blue) or −92 mV (red) (n = 10 cells, N = 4 mice, p = 0.0039, **p < 0.005, two-sided Wilcoxon signed rank test). b, e, i, j Data are presented as means ± S.E.M. pSBC putative single-bouquet cell, pNGF putative neurogliaform cell, pSOM⁺ putative somatostatin-expressing cell, pPV⁺ putative parvalbumin-expressing cell, p5HT₃R⁺ putative serotonin 3A receptor-expressing cell, PN pyramidal neuron, IPSC inhibitory postsynaptic current, EPSC excitatory postsynaptic current.