Rho signaling promotes cell excitability and neurotransmission.

Gαq signaling through Trio RhoGEF and Phospholipase C effectors promotes neurotransmitter release at synapses. Whether activated Rho and Phospholipase C signaling acts through shared or independent pathways remains unclear. We use the egg-laying circuit of the nematode worm, Caenorhabditis elegans, which is regulated positively by Gαq signaling and negatively by Gαo signaling, to determine the role of Rho GTPase in G-protein regulation of neural circuit excitability. We previously showed that Trio signals in both the presynaptic hermaphrodite-specific command neurons (HSNs) and the postsynaptic egg-laying vulval muscles they innervate to promote egg laying. Here, we show that its effector Rho similarly signals both presynaptically and postsynaptically. Expression of constitutively active Rho-1(G14V) in either the HSNs or vulval muscles increased their Ca2+ activity and stimulated egg laying. Conversely, reducing Rho signaling inhibited HSN Ca2+ activity and egg laying. Animals lacking Rho function in HSN still had vulval muscle Ca2+ activity that supported contraction and egg release, although this Ca2+ activity lacked the enhancement associated with HSN neurotransmitter release, suggesting it was largely driven by stretch-dependent feedback. Together, these results show that Rho signals in both the HSNs and vulval muscles promote excitability and egg laying.