Fig. 2: D-MNs favor forward locomotion through activating UNC-49 GABA_A receptor in AVA interneurons.

a Optogenetic activation of D-MNs suppressed spontaneous postsynaptic currents (sPSCs) in VA5 (held at −60 mV) without causing an evoked inward current. All worms were treated with all-trans retinal except for those of the wild-type (wt) control group (indicated). The bar graph shows the percentage of sPSC reduction compared with the pre-stimulation period. Only slow and large sPSCs, which result from synaptic transmission from AVA³⁴, were quantified. In quantifying the effect of blue light stimulation on sPSCs, the entire interval showing an apparent lack of events was used for wt (with retinal) but only the interval matching the blue light pulse was used for the remaining groups. Compared with wt, p = 0.000 for all groups. b Optogenetic activation of D-MNs evoked outward current in AVA (held at −10 mV) and caused AVA hyperpolarization in wt but not in either unc-49(e407) or the AVA-targeted unc-49 RNAi strain. Compared with wt, p = 0.000 for both groups. c Gabazine (500 µM) abolished AVA outward current evoked by optogenetic activation of D-MNs. Compared with Pre-gabazine, p = 0.000 for both groups. d Inhibitory sPSCs were greatly reduced in the unc-49 mutant and RNAi strains. Compared with wt, p = 0.000 for Inhibitory sPSCs of both groups, but 0.777 and 0.844 for excitatory sPSCs of unc-49 and RNAi, respectively. e Expression of GFP under the control of unc-49 promoter in a strain with AVA neurons labeled by mStrawberry resulted in AVA colabeling by both fluorescent proteins. The displayed images represent >20 transgenic worms. Scale bar = 10 µm. f Comparison of locomotor kinematics between wt and the unc-49 RNAi strain. p = 0.044 Forward distance, 0.044 backward distance, 0.049 backward/forward ratio, 0.424 forward speed, and 0.960 backward speed. g Diagram showing a closed-loop circuit that includes AVA, A-type cholinergic motor neurons, and D-MNs. The horizontal blue lines in a–c indicate the times (2 or 5 s) of blue light stimulation. The asterisks indicate significant differences (*p < 0.05, ***p < 0.001) based on either one-way ANOVA with Tukey’s post hoc test (a, b, d), paired two-sided t-test (c), or unpaired t-test (f). The numbers inside brackets indicate sample size (n). n = numbers of independently recorded cells in a–d, but numbers of individual worms in f. Data are presented as mean values ± SEM. Source data are provided as a Source data file.