Fig. 3.

When activated by the mechanosensory VCNs, CPN2 intraburst firing rate is altered by CPG feedback. A: in an example experiment after VCN stimulation with feedback intact (Ai), CPN2 fired at ~38 Hz during protraction (Pro., black bar) and fired only a few action potentials during retraction (Ret., white bar). CPN2 was recorded via intra-axonal impalement in the nerve (stn) it projects through just before entering the STG. CPN2 instantaneous firing rate is plotted above the traces. After VCN stimulation in the absence of feedback (Aii), CPN2 fired at an average frequency of ~16 Hz. The variability in instantaneous firing rate likely resulted from other synaptic input to CPN2 including the AGR sensory neuron which remained spontaneously active in the absence of feedback (Hedrich et al. 2009; Norris et al. 1994; Smarandache et al. 2008; Städele and Stein 2016). B: across preparations, the average CPN2 intraburst firing rate was higher during VCN protraction (Pro., black bar, n = 13) than VCN retraction (Ret., white bar, n = 11) and higher during protraction than its average firing rate in the no-feedback condition (NF, gray bar, n = 10). The retraction intraburst firing rate does not include the pyloric-timed interruptions in firing. ***P < 0.01; ^nsnonsignificant.