Nobel laureates '2000 in Physiology and Medicine were Arvid Carlsson, Paul Greengard, and Eric Kandel. Their discoveries have been crucial for our understanding of the mechanisms of signal transduction inside and between nerval cells. Carlsson discovered that dopamine is a neurotransmitter the substance, which actively takes part in the signal transduction in synapses. He showed that its depletion results in movement dysfunction similar to one observed in Parkinson's disease. The symptoms could be treated with the dopamine precursor: L-dopa.