Monoaminergic Orchestration of Motor Programs in a Complex C. elegans Behavior
(A, B) SER-2 expression in cholinergic (Pacr-2::SER-2) or GABAergic (Punc-47::SER-2) motor neurons alters the rate of paralysis of ser-2 mutants on aldicarb drug plates. All genotypes paralyze at a similar rate on drug plates containing only 0.5 mM aldicarb (A), yet drug plates containing both 30 mM tyramine and 0.5 mM aldicarb causes paralytic resistance (Pacr-2::SER-2) or hypersensitivity (Punc-47::SER-2) (B). Aldicarb experiments were conducted on nematode growth media (NGM) plates. 30 mM tyramine dissolved in NGM agar does not inhibit locomotion. SER-2 was expressed in ser-2(pk1357) mutant animals. Each data point represents the mean percentage of animals immobilized by aldicarb scored every 30 min ± SEM for at least four trials, totaling a minimum of 60 animals. (C, D) Representative endogenous inhibitory postsynaptic currents (IPSCs) recorded from ventral body wall muscles. +/+, unc-29; acr-16 double mutants that lack excitatory neurotransmission at the NMJ are wild-type for the ser-2 locus. ser-2, unc-29; acr-16; ser-2(pk1357) triple mutants. (E, F) Tyramine application decreased the rate of IPSCs in +/+ (n = 6), but not ser-2 mutants (n = 5). Arrow depicts tyramine application time point. Each point represents the IPSC frequency calculated over a 5-s time window as indicated. The red points correspond to the displayed samples in (C) and (D), respectively. Dashed lines show average frequency before tyramine application and during the stabilized tyramine response period. (G) Average IPSC frequency after tyramine application plotted relative to IPSC frequency prior to tyramine exposure. Values were normalized to average frequency observed in control recordings in the absence of tyramine. (H) Average amplitude of IPSCs after tyramine application plotted relative to average amplitude prior to tyramine exposure. Error bars depict SEM. Statistical differences calculated from +/+: *p<0.05, two-tailed Student's t test.