Figure 8.

Vulval muscle activity and egg accumulation promote HSN burst firing. A, Adult animals (24 h) expressing HisCl in the postsynaptic vulval muscles (vm) and GCaMP5/mCherry in the presynaptic HSNs were placed onto NGM plates with (blue, bottom) or without histamine (green, top) for 3–4 h to induce muscle silencing and cessation of egg laying. Animals were then moved to plates without histamine and allowed to recover for 30 min before HSN Ca²⁺ imaging. HSN Ca²⁺ imaging was also performed on adults not removed from histamine (blue, middle). Arrowheads indicate egg-laying events. B, Cumulative distribution plots of instantaneous HSN Ca²⁺ transient peak frequencies (and intertransient intervals) on histamine (open blue circles), and after histamine washout (filled blue circles) compared with untreated controls (filled green circles). *p < 0.0001, Kruskal–Wallis test. C, Scatter plots show fraction of time spent by each individual with frequent HSN Ca²⁺ transients characteristic of the egg-laying active state (<30 s) in untreated controls (green circles), on histamine (blue open circles), and after histamine washout (blue circles). Error bars indicate 95% confidence intervals for the mean. *p ≤ 0.0061, one-way ANOVA.