ABSTRACT
Paul Greengard has shown that many types of neurotransmitters in the brain exert their physiological effects by stimulating chemicals called "second messengers", which cause the phosphorylation of key proteins involved in a wide range of intracellular processes. In the mid-1950s, Sutherland had examined how the pancreatic hormone glucagon breaks down glycogen in the liver to provide glucose for energy. Greengard was inspired by Sutherland's research to undertake the highly ambitious task of looking for second messengers in the nervous system and establishing whether cAMP played a role in neurotransmitter action. The concept of slow synaptic neuro transmission would play a pivotal part in Greengard's theorising over the subsequent years. Soon after Greengard's laboratory had established the role of cAMP in several types of neural functioning, another substance was recognised as having second messenger actions in the brain and some other tissues. This was cyclic guanosine monophosphate, which was shown to regulate a different type of kinase inside the cell.
