Autoradiography of antidepressant binding sites in the human brain: localization using [3H]imipramine and [3H]paroxetine

Abstract

[3H]Imipramine and [3H]paroxetine were used to label sites associated with serotonin uptake mechanisms in post-mortem brain tissue from control subjects. The anatomical localization of these sites was examined by autoradiography and densities measured by microdensitometry. We found [3H]imipramine binding to increase with age in the cortex and amygdala, but to be independent of gender and post-mortem delay. Preliminary results indicate that the binding of both [3H]imipramine and [3H]paroxetine is diminished in the brain of patients treated with imipramine. The distribution of [3H]imipramine and [3H]paroxetine high-affinity binding sites was very similar, and correlated well with the distribution of serotonergic presynaptic markers in the brain. The highest densities of binding sites were found in the raphé nuclei and the midline thalamic nuclei. Other structures presenting high levels of binding were the substantia nigra, nucleus interpeduncularis, locus coeruleus, nucleus nervi hypoglossi, nucleus nervi facialis, mammillary bodies and other parts of the hypothalamus. In contrast, regions such as the neocortex, hippocampus, amygdala and cerebellum showed low densities of [3H]imipramine and [3H]paroxetine binding sites. This distribution seems to indicate that the ascending serotonergic pathways are the main site of action of antidepressants.