Potential roles of NCAM/PSA-NCAM proteins in depression and the mechanism of action of antidepressant drugs.

Recently, it has been proposed that abnormalities in neuronal structural plasticity may underlie the pathogenesis of major depression, resulting in changes in the volume of specific brain regions, including the hippocampus (HIP), the prefrontal cortex (PC), and the amygdala (AMY), as well as the morphology of individual neurons in these brain regions. In the present survey, we compile the data regarding the involvement of the neural cell adhesion molecule (NCAM) protein and its polysialylated form (PSA-NCAM) in the pathogenesis of depression and the mechanism of action of antidepressant drugs (ADDs). Elevated expression of PSA-NCAM may reflect neuroplastic changes, whereas decreased expression implies a rigidification of neuronal morphology and an impedance of dynamic changes in synaptic structure. Special emphasis is placed on the clinical data, genetic models, and the effects of ADDs on NCAM/PSA-NCAM expression in the brain regions in which these proteins are constitutively expressed and neurogenesis is not a major factor; this emphasis is necessary to prevent cell proliferation and neurogenesis from obscuring the issue of brain plasticity.