Fig. 1.

Octuple recording from GCs and PV⁺ interneurons in the dentate gyrus. a Octuple recording from five GCs and two PV⁺ interneurons (seven cells successfully recorded). Infrared differential interference contrast video micrograph of the dentate gyrus in a 300-µm slice preparation, with eight recording pipettes. Shaded areas represent the 2D projections of cell bodies (blue, GCs; red and yellow, PV⁺ interneurons). Blue dashed lines, boundaries of GC layer. b Partial reconstruction of one GC and two PV⁺ interneurons in the same recording as shown in (a). Cells were filled with biocytin during recording and visualized using 3,3′-diaminobenzidine as chromogen. For clarity, only the somatodendritic domains were drawn for the PV⁺ interneurons. Insets, biocytin-labeled putative synaptic contacts, corresponding to boxes in main figure. c Connectivity matrix of an octuple recording (all eight cells successfully recorded). Subpanels on the diagonal (AP traces) represent the presynaptic cells, subpanels outside the diagonal (EPSC or IPSC traces) indicate postsynaptic cells. In this example, 56 connections were tested; 7 excitatory GC–PV⁺ interneuron connections, 7 inhibitory PV⁺ interneuron–GC connections, and 42 connections between GCs. Brief transients in a subset of traces represent capacitive coupling artifacts, as shown in previous publications^{5, 14}. d Expanded view of presynaptic APs and postsynaptic currents, corresponding to the boxed areas in (c). In this octuple recording, an inhibitory synaptic connection was identified between the PV⁺ interneuron (red) and GC 5 (blue) and an excitatory synaptic connection was found between GC 1 (blue) and the PV⁺ interneuron (red). The presence of a unidirectional excitatory GC–PV⁺ interneuron connection and a unidirectional inhibitory PV⁺ interneuron–GC connection documents the existence of lateral inhibition in this recording. e Coexistence of different synapses in an octuple recording. In this recording, an excitatory GC–PV⁺ interneuron connection, an inhibitory PV⁺ interneuron–GC connection, a chemical inhibitory connection between the PV⁺ interneurons, and an electrical connection between the PV⁺ interneurons were found (from left to right). Same recording as in (a) and (b)