Fig. 6

Feedforward excitation between esV2a interneurons and convergence onto pMNs. (A) Dual whole-cell patch-clamp recording from a rostral and a caudal esV2a interneuron that were electrically coupled. (B) Chemical synaptic transmission occurred only from the rostral to the caudal esV2a interneuron. (C) Quantification of the mean amplitude of synaptic potentials between esV2a interneurons. The Left graph represents data from rostral to caudal esV2a interneuron as mean ± SD, n = 6; one-way ANOVA, P = 6 × 10⁻⁶ for control vs. d-tubocurarine (Cur); P > 0.05 for d-tubocurarine vs. Cd²⁺. The Right graph represents data from caudal to rostral esV2a interneuron as mean ± SD, n = 6; one-way ANOVA, P > 0.05 for control vs. d-tubocurarine; P > 0.05 for d-tubocurarine vs. Cd²⁺. Each dot represents the data from single neurons. (D) Reconstruction of the two recorded esV2a interneurons (Upper). (Lower) Coexpression of VAChT (green) and Cx36 (red and indicated by a white arrow) at the crossing point of their axons (blue) that represents the presumed site of contact located in the segment of the caudal esV2a interneuron. These images correspond to the region indicated in the box of the Upper panel. The axon of esV2a interneurons is indicated by the dashed lines. (E) Triple whole-cell patch-clamp recordings from two rostral esV2a interneurons and a pMN. Each esV2a interneuron produced subthreshold EPSPs in the pMN, which was recruited by the convergent input from the two interneurons. Two superimposed traces are shown to indicate the reliability of firing and variability in spike amplitude. Black arrows indicate the peaks of two spikes. (F) Quantification of the mean EPSP amplitude induced in pMNs by each esV2a interneuron. The graph represents mean ± SD, n = 13; paired t test, P = 0.8 × 10⁻⁴. Each dot represents the data from a single neuron.