 The complex regulation of respiratory rhythm involves the integration of multiple signaling molecules and the activation of numerous diverse metabotropic and ionotropic receptors.These include norepinephrine, serotonin, acetylcholine, substance P, ATP, TRH, somatostatin, dopamine, endorphins, and adenosine, which in turn activate g-protein coupled receptors to produce the diverse responses mediated by the pre-Bötzinger complex.Nonpacemaker and pacemaker neurons involved in inspiration are stimulated by NE.