Role of cyclic GMP in olfactory transduction and adaptation

The detection of odor molecules by vertebrate olfactory receptor neurons (ORNs) involves signal transduction mechanisms that are thought to occur primarily through a cyclic adenosine monophosphate (cAMP)-mediated second messenger pathway. There has been intense debate whether cAMP is the sole second messenger responsible for all excitation and adaptation. The recent identification of a distinct form of odor adaptation that depends on the carbon monoxide/cyclic guanosine monophosphate (cGMP) second messenger system demonstrates that cAMP alone cannot account for all phases of adaptation and that multiple second messenger pathways exist in ORNs to perform distinct but closely related olfactory functions.