Psychopharmacology

“The third area of scientific development that contributed to the advent of modern psychopharmacology was the discovery of chemical transmission at neural junctions in the central nervous system. . . . These [1904-1914] observations suggested a possible physiological significance of acetylcholine, particularly as a parasympathetic neurotransmitter. At the time, however, acetylcholine had not been shown to be normally present in animal tissue. Conclusive evidence that the effects of parasympathetic nerve stimulation are mediated by liberation of a chemical transmitter that resembled acetylcholine in all respects examined was provided in the early 1920s by Loewi, who showed that after simulating the vagus nerve [which slows heart rate] to the frog heart, fluid from the heart inhibited a test heart. In 1929 the presence of naturally occurring acetylcholine in animal tissue was first reported. Conclusive evidence that sympathetic nerves released a chemical transmitter having the properties of adrenaline was provided by Cannon and Bacq in 1931. . . . By the end of the 1950s the weight of evidence in support of chemical transmission in the CNS was sufficient to convince even strong early advocates of the electrical hypothesis (Eccles, 1959). With the discovery of chemical transmission in the CNS, identification of the central neurotransmitters became a major focus of research. By 1960 numerous substances, including acetylcholine, norepinephrine, dopamine, and serotonin, were considered likely brain neurotransmitters” (Baumeister & Hawkins, 205). . . . “in each case, the development in understanding the mechanisms of action of psychotropic drugs depended critically on the discovery of central neurotransmitters. At the same time, the evolving understanding of drug mechanisms of action helped to clarify the physiological significance of neurotransmitters. For example, reserpine depletes monoamines and produces immobility in animals. This immobility is reversed by L-dopa, suggesting a physiologic function for dopamine in movement. . . . The discovery of chemical transmission at neuronal junctions in the CNS was a foundational event in the rise of psychopharmacology. . . . Without the knowledge that junctional transmission in the brain was chemical, along with the corollary idea that disturbances in neurotransmission underlie mental illness, psychopharmacology would have remained purely empirical” (206).