catecholamine hypothesis
the hypothesis that deficiencies in the catecholamine neurotransmitters norepinephrine, epinephrine, and dopamine at receptor sites in the brain lead to a state of physiological and psychological depression, and that an excess of such neurotransmitters at these sites is responsible for the production of mania. The catecholamine hypothesis underlay the development of the early tricyclic antidepressants in the late 1950s, as it had been known that these compounds inhibited the reuptake of norepinephrine into presynaptic neurons. Despite numerous shortcomings, the catecholamine hypothesis, and the related monoamine hypothesis, became the dominant hypotheses in the biological treatment of depression in the last half of the 20th century.