Fig. 5: Prolonged inhibition in layer_III–V pyramidal cells is mediated by the neuromodulator peptide SOM.

a Decay and rise times similarities of PSPs elicited by PV⁺ and SOM⁺ interneurons indicate classical fast GABAA receptor-mediated inhibition. The averages (thick lines) and S.E.M. (thin lines) of PSPs after short (3 ms) light pulses in PV-ChR2 (blue) and SOM-ChR2 (red) MEC. Layer_III–V pyramidal cells held at resting membrane potentials. Inset: rise and decay times of individual pyramidal cells in PV-ChR2 (blue) and SOM-ChR2 (red) animals. b Both in SOM-ChR2 and PV-ChR2 animals, the PSPs (red, blue lines, respectively) can be completely eliminated by gabazine (black traces). c Action potentials (elicited by depolarization) in layer_III–V pyramidal cells are stopped by 100 ms light pulse for different time in SOM-ChR2 (red), PV-ChR2 (blue), and SOM-ChR2+/SST4 KO (black) animals. d Statistic showing MEC deep principal cells firing latencies (as shown in c) after optogenetic stimulation of SOM-ChR2 (red), PV-ChR2 (blue), and SOM-ChR2+/SST4 KO (black) animals. e Population averages of the light-inhibited pyramidal cells in in vivo awake mice. Note that plots for SOM⁺ (red) and PV⁺ (blue) are same as in Fig. 3b for comparison with SST4 KO animals (black). f Statistics showing 50% recovery times of firing after light-induced inhibition in SOM⁺ (red), PV⁺ (blue), and SST4 KO (black) animals. g Representative voltage responses of MEC layer_II (up) and deep layer (bottom) principal cell upon step current injections (150 and −200 pA) under control conditions (left) and after bath application of 1 µM J-2156 (right, green). h Firing frequencies of MEC layer_II (up) and deep layer (bottom) principal cells upon current injections under control and J-2156-treated conditions. *p < 0.05, **p < 0.01, ***p < 0.001, paired Student’s T test for in vitro and Wilcoxon rank-sum test for in vivo experiments.