Quantitative autoradiographic localization of [3H]imipramine binding sites in the brain of the rat: relationship to ascending 5-hydroxytryptamine neuron systems.

Quantitative autoradiography shows that there is a close relationship between [3H]imipramine binding sites and the distribution of 5-hydroxytryptamine (5-HT) neurons in the rat brain. High labeling is observed in the midbrain raphe nuclei, the areas of the dopamine cell groups of the substantia nigra and of the ventral tegmental area of Tsai, the ventral amygdaloid nucleus, the midline thalamic area, and parts of the hypothalmus. Thus, antidepressant drugs that have high affinity for [3H]imipramine binding sites can exert an influence at the 5-HT cell body as well as at the 5-HT nerve terminal level. The present results underline the possibility that the 5-HT and dopamine hypotheses for the mechanism of action of antidepressant drugs are not mutually exclusive, because both 5-HT and dopamine neurons can be regulated by large numbers of [3H]imipramine binding sites.