Chemical Communication: Linking Behavior and Physiology

Abstract

How does physiological state affect the reproductive behavior of an organism? Two new studies in Caenorhabditis elegans implicate an ancient serotonergic neuronal circuit in the link between these two outputs - reproductive behavior and physiology.

Figure 1.. The HSN–vm2 circuit links the behavioral and physiological outputs of ascr#10 signaling.

(A) The ascarosides ascr#10 and ascr#3 are structurally identical with the exception of a single carbon–carbon bond (blue arrow) within the fatty-acid-derived side chain. (B) In the absence of ascr#10, there is no upregulation of the serotonin biosynthesis gene tph-1 in either NSM or HSN neurons, allowing the RIF and AIY neurons to remain active. This results in exploratory behavior and a slowing of germline development. (C) In the presence of ascr#10, after the HSN–vm2 network is completely formed, tph-1 levels increase in the HSN neurons. This results in serotonin (5HT) release and inhibition of the RIF and AIY neurons via the serotonin-gated chloride channel MOD-1. Exploratory behavior decreases, and the rate of germ cell production is increased. The HSN–vm2 circuit (blue) is critical in linking the behavioral and physiological outputs of ascr#10. Upon forming synaptic connections during development, the HSN neurons stimulate the vm2 vulval muscle cells to initiate egg laying. Conversely, the vm2 cells then report back to the HSN neurons on the status of egg laying. This network allows ascr#10 sensation to initiate tph-1 transcription in the HSN neurons.