Figure 3: Pyramidal and MC form an inhibitory feedback loop.

(a) Connectivity between PC and MCs, determined from dual patch clamp recordings in 55 X98-SST mice, showing the percentage of connected pairs (%) and the number of tested paired records (n). Very few PC–PC connections were detected. (b) Single spikes of MCs (green) reliably evoked small IPSPs in a PC (blue). Action potentials were initiated by brief current injections (1–2.5 nA for 1–2.5 ms (b,d)). Average current traces in red, stimulation artifacts on the MC voltage trace blanked. (c) Transfer rate (n=11), IPSC amplitude (n=45 pairs) and IPSP absolute amplitude (n=21 pairs) from responses to single spikes at MC-to-PC synapses. Red horizontal bars are median values. Transfer rates from automatically detected synaptic events, recorded with a Cs-Glu based internal solution. Amplitudes from averages of responses recorded using a low-Cl K-Glu internal solution (cf. Methods). (d) Single spikes of PCs (blue) did not reliably evoke EPSPs in a MC (green). The mean EPSP amplitude (red) was very low. (e) Transfer rate (n=44), EPSC absolute amplitude (n=38) and EPSP amplitude (n=8) from responses to single spikes at a PC-to-MC synapse. Red horizontal bars give median values. Transfer rate and potency from automatically detected synaptic events, recorded with a low-Cl K-Glu internal solution (methods). Efficacy was calculated as transfer rate × potency and used as measure of average amplitude.