Fig. 3.

Rules of excitatory and inhibitory connectivity in GC–PV⁺ interneuron networks. a Unitary EPSCs, with individual synaptic responses (gray) and average trace (red, 15 traces) in a representative GC–PV⁺ interneuron pair. b GC–PV⁺ interneuron connection probability plotted versus intersomatic distance. Connection probability was determined as the ratio of the number of found connections over that of all possible connections in a given distance range. Error bars represent 95%-confidence intervals estimated from a binomial distribution. Data points were fit with a sigmoidal function; shaded area indicates the distance range in which connection probability decayed to half-maximal value (space constant). Red dashed line, maximal connection probability. Maximal connection probability (c_max) was 11.3%, and space constant (d_half) was 144 µm. c Peak amplitude of unitary EPSCs at GC–PV⁺ interneuron synapses, plotted against intersomatic distance. Data points were fit by linear regression; dashed lines indicate 95%-confidence intervals. d–f Similar plots as shown in (a–c), but for IPSCs generated at inhibitory PV⁺ interneuron–GC synapses. Maximal connection probability was 28.9%, and space constant was 215 µm. g Bootstrap analysis of maximal connection probability and space constant. Histograms indicate distributions of c_max (left) and d_half (right) for 10,000 bootstrap replications of the inhibitory PV⁺ interneuron–GC connections. Red arrows indicate experimental mean values for GC–PV⁺ interneuron synapses. h Number of reciprocally coupled GC–PV⁺ interneuron pairs (excitatory and inhibitory synapse; “recurrent inhibition motif”) and unidirectionally coupled PV⁺ interneuron–GC pairs (inhibitory synapse only; “lateral inhibition motif”). Note that the number of lateral inhibition motifs was almost 10-times higher than that of recurrent inhibition motifs, demonstrating the high abundance of lateral inhibition in the dentate gyrus microcircuit