Muscle-directed mechanosensory feedback activates egg-laying circuit activity and behavior in C. elegans

Mechanosensory feedback of internal state regulates numerous bodily processes including feeding, defecation, and reproduction. However, how mechanosensory feedback signals to modulate neural circuits and coordinate these behaviors is incompletely understood. Here, we use the egg-laying circuit of C. elegans to test our hypothesis that mechanosensory feedback of egg accumulation promotes the active reproductive behavior state. Using an acute gonad microinjection technique to mimic changes in pressure and stretch resulting from germline activity and egg accumulation, we find that injection rapidly stimulates Ca2+ activity in both neurons and muscles of the egg-laying circuit. Injection-induced vulval muscle Ca2+ activity requires L-type Ca2+ channels but is independent of presynaptic input. Direct mechanical prodding activates the vulval muscles, suggesting they are the proximal targets of the stretch-dependent stimulus. Our results show that egg-laying behavior in C. elegans is regulated by a stretch-dependent homeostat that scales postsynaptic muscle responses with egg accumulation in the uterus.