Re-coding of G protein-coupled receptor signaling enables emergent cellular behavior.

All cells face the challenge of integrating multiple extracellular signals to produce relevant physiological responses. Different combinations of G protein-coupled receptors, when co-expressed, can lead to distinct cellular outputs, yet the molecular basis for this co-operativity is controversial. One such interaction is the reversal, from inhibition to excitation, at the dopamine D2 receptor in the ghrelin receptors presence, relevant for defecation control. Here we demonstrate that this reversal of dopamine D2 activity, to excitatory, occurs through a dominant switch in downstream signaling. This dominant switch, mediated by downstream signaling, enables fidelity in cellular responses not possible under alternative models, and provides an explanation for previously unresolved observations. Importantly, the switch in D2 signaling does not require ghrelin receptor agonism, rather its constitutive activity, thus accounting for the importance of central nervous system-ghrelin receptor in the absence of endogenous ligands. This re-coding has important implications for our understanding of how atypical receptor pharmacology can occur as well as how sequential signaling at individual neurons may be encoded to produce new outputs.