Gases as biological messengers: nitric oxide and carbon monoxide in the brain.

In a remarkably brief period of time, NO and CO have been recognized as putative neurotransmitters. These two novel messenger molecules have greatly expanded the criteria for candidacy of a chemical for the status of neurotransmitter and our notions about how synaptic transmission takes place. The involvement of NO and CO in several important aspects of neuronal function suggests that agents affecting the synthesis, transactions, and disposition of these gases are bound to have clinical relevance.