Figure 6. Distinct roles of serotonin receptors in pumping stimulated by exogenous serotonin.

(a) Average pumping rate of wild-type (N2) worms, tph-1 mutants and a range of serotonin receptor mutants at different concentrations of serotonin (5-HT) in bacteria-free media. Sample sizes are given in Supplementary Table 2. (b,c) The average fraction of time spent in long pauses (b) and fast pumping (c) by wild-type (N2) worms as a function of the concentration of serotonin in bacteria-free media. (d,e) The average fraction of time spent in long pauses (d) and fast pumping (e) by wild-type (N2) worms, tph-1 mutants and a range of serotonin receptor mutants in bacteria-free media supplemented with 5 mM serotonin. Here the threshold rate for fast pumping was taken to be 160 pumps per min for ser-4 worms and 200 pumps per min otherwise (based on Supplementary Fig. 6A,F). Error bars as in Fig. 2. Statistical significance indicated as in Fig. 5. (f) Summary of the distinct roles of serotonin receptors. In food-driven pumping, SER-1 is involved in promoting pumping bursts, presumably with contributions from SER-4. The stimulation of pumping by exogenous serotonin requires the SER-7 and SER-4 receptors.