Dopamine.

Dopamine was first described by George Barger, James Ewens, and Henry Dale in 1910 as an epinephrine-like monoamine compound. Initially believed to be a mere precursor of norepinephrine, it was mostly ignored for the next four decades (Figure 1A). However, in the 1950s Kathleen Montagu showed that dopamine occurred in the brain by itself, and a series of studies by Arvid Carlsson and collaborators demonstrated that dopamine is a bona fide neurotransmitter, a finding that would earn Carlsson the 2000 Nobel Prize in Physiology and Medicine. In a landmark experiment, he pharmacologically blocked all dopamine neurotransmission in rabbits, which rendered them completely paralyzed, and then fully recovered their behavior with an injection of the dopamine precursor L-DOPA, demonstrating that dopamine was essential for self-initiated movement (Figure 1B). A similar effect was quickly reproduced by Oleg Hornykiewicz and collaborators in human Parkinsonian patients. Within a few years, dopamine jumped from relative obscurity to being critical for life as we know it.