The absence of monosynaptic GABAergic connection between SuM and CA3 PV⁺ neurons. A, A schematic view of SuM-to-CA3 circuit and experimental configuration showing target recording of PV⁺ neurons. PV⁺ neurons provide mutual inhibition. B, Voltage-clamp recording traces from a PV⁺ neuron show light-evoked IPSC (hold potential = 0 mV) and EPSC (holding potential = –75 mV) in the absence (black) and presence (red) of DNQX/APV. C, Expanded view shown in B. IPSC onset is slower than EPSC onset. D, Group data of light-evoked IPSC amplitude in the absence and presence of DNQX/APV. n = 5 cells/5 slices/2 mice. *p < 0.05 (paired t test). E, Group data of light-evoked EPSC latencies (n = 16 cells/12 slices/6 mice) versus IPSC (n = 5 cells/5 slices/2 mice). ***p < 0.001 (unpaired t test).