Neurochemical correlates of major depression in primary dementia

Biogenic amine neurotransmitters and metabolites as well as choline acetyltransferase activity were quantified in eight brain regions from 37 demented patients, with or without major depression, and 10 controls with no history of dementia or depression. The middle frontal and temporal cortex, prosubiculum and entorhinal cortex of the hippocampus, substantia nigra, thalamus, amygdala, and caudate were examined. Demented patients with major depression exhibited a 10-fold to 20-fold reduction in the level of norepinephrine in the cortex, along with relative preservation of choline acetyltransferase activity in subcortical regions, compared with demented patients who were not depressed. Serotonin levels were reduced in all eight brain regions, but the reduction did not reach statistical significance in any region examined. A para-doxical increase in dopamine levels was observed in the entorhinal cortex of depressed, demented patients, although no consistent pattern of change in the level of this neurotransmitter emerged across brain regions. Our results indicate that the development of major depression in primary dementia is associated with a profile of concurrent neurochemical changes that is largely consistent with existing neurochemical hypotheses of idiopathic affective disorders, and qualitatively distinct from that associated with primary dementia.