Abstract
Caenorhabditis elegans egg laying is a two-state behavior modulated by sensory input. Feedback of egg accumulation in the uterus drives activity of the serotonergic HSN command neurons to promote the active state, but how aversive sensory stimuli signal to inhibit egg laying is not well understood. We find the Pertussis Toxin-sensitive G protein, Gαo, signals in HSN to inhibit circuit activity and prolong the inactive behavior state. Gαo signaling hyperpolarizes HSN, reducing Ca2+ activity and input into the postsynaptic vulval muscles. Loss of inhibitory Gαo signaling uncouples presynaptic HSN activity from a postsynaptic, stretch-dependent homeostat, causing precocious entry into the egg-laying active state. NLP-7 neuropeptides signal to reduce egg laying both by inhibiting HSN and by activating Gαo in cells other than HSN. Thus, Gαo integrates diverse signals to maintain a bi-stable state of electrical excitability that dynamically controls circuit activity and behavior output in response to a changing environment.