Fig. 3

Synaptic connections between clonal and nonclonal neuron pairs in the barrel cortex. a Differential interference contrast image of a brain slice with two recording electrodes in a layer 4 barrel. Scale bar: 100 μm. b Green fluorescent protein (GFP)-positive cells in layer 4. Dashed line indicates a barrel. Scale bar: 50 μm. c Proportion of GFP-positive neurons in the analyzed area at each age. The number of tested columns is 8, 18, and 18 for P9–11, P13–16, and P18–20, respectively. P = 0.51 (Kruskal–Wallis test). d Representative average traces (n = 20) of action potentials evoked by brief depolarizing voltage pulses in one cell (pre) and resultant excitatory postsynaptic currents in the other (post) with one-way (upper) or reciprocal (lower) connections between GFP-positive excitatory neurons in layer 4 (P-P pair, left) and GFP-positive and -negative neurons (P-N pair, right) in P18–20 wild-type chimeric mice. e Percentage of P-P (left) and P-N (right) pairs with one-way (blue), reciprocal (magenta), or no (gray) connections; the number of recorded pairs is shown on each bar. Number of mice for P-P pairs: P9–11(n = 7), P13–16 (n = 10), P18–20 (n = 12); P-N pairs: P9–11(n = 6), P13–16 (n = 11), P18–20 (n = 9). *P < 0.05, ***P < 0.001: connection probabilities in different age groups (χ² test with a 3 × 2 matrix after Bonferroni correction). f, g Developmental changes in the connection probability (f) and the proportion of reciprocal connections in connected pairs (reciprocity, g). **P < 0.01: P-P versus P-N pairs at the same age (Fisher’s exact test)