AC activity is regulated by different receptors, including dopamine, opiate, adenosine, muscarinic cholinergic, corticotropin-releasing factor (CRF) adrenergic, and serotonergic receptors. These receptors interact with either stimulatory (Gs) or inhibitory (Gi) G protein subtypes, resulting in stimulation or inhibition of AC.89 On the other side of the cAMP signaling cascade, phosphodiesterases can inactivate cAMP through hydrolysis into AMP. There are two known targets of cAMP in mammals, the cAMP-dependent protein kinase (PKA) and the cAMP-gated ion channel (predominantly found in the olfactory neurons). The production of cAMP depresses the activity of PKA, which then modulates intracellular metabolism, receptor, or ion channel function, and gene expression in various cells and tissues.88,90,91 cAMP-responsive binding element (CREB) is one example of a transcription factor that can be modulated in its function by the cAMP signaling cascade.
