Paul Greengard shared with Arvid Carlsson and Eric R. Kandel the 2000 Nobel Prize in physiology because of his discovery of the cellular signal pathways used by dopamine as well as by a number of other neurotransmitters. Neurotransmitters are biochemical molecules that trigger a cascade of stimuli in neural cells. These signal pathways are biochemical events mediated by intracellular enzymes and proteins, and are generally termed signal transduction. The understanding of such pathways in the nervous system is of fundamental importance for the identification of the causal events associated with a series of mental and behavioral disorders and, consequently, for the development of new drug therapies. Dopamine, noradrenaline, and serotonin are neurotransmitters of the so-called slow synaptic transmission (SST), which implies that the changes caused in the nerve cell by these molecules may last from a few seconds up to several hours. SST is responsible for several basal functions...