A jack of all trades: Hermaphrodite-specific serotonergic neuron in C. elegans

How does a single neuron type shape both short- and long-term behavior? A study reveals how co-transmission by two hermaphrodite-specific neurons (HSNs) of Caenorhabditis elegans produces both transient and long-lasting effects on its egg-laying behavior. A key question in neuroscience is how neurons and circuits integrate information to drive behavior. In the nematode C. elegans, locomotion, feeding, defecation and egg-laying motor programs are all generated by a simple nervous system consisting of 302 neurons whose connectivity patterns are fully described (White et al. 1986). Egg-laying behavior allows dispersal of eggs in the most appropriate locations. The egg-laying circuit consists of two hermaphrodite-specific serotonergic neurons (HSNs) and six ventral cholinergic C-neurons (VCs) connected to the vulval muscle. In addition, uv1 neuroendocrine cells mechanically respond to egg laying by the release of tyramine and neuropeptides. Together, they produce a rhythmic behavior modulated by environmental cues that alternates between egg-laying phases and resting periods (Hardaker et al. 2001; Ringstad and Horvitz 2008; Fenk and de Bono 2015). How can such a simple circuit generate rhythmic and regulated behavior?