(Description) Figure 11 The neurotrophic hypothesis of mood disorders. The green area represents a neuronal cell. Within the cell is a box representing neuroplasticity and neuron health. Minus signs (-) indicate factors that damage neuroplasticity and neuron health, while plus signs (+) indicate factors that promote it. Some factors deleterious to neuroplasticity and neuron health are represented in the top half of the figure. For instance, low serotonin levels, and stress and depression, reduce the level of BDNF, weakening (as indicated by the broken line) its positive impact on neuroplasticity and neuron health; stress and depression also raise the level of cortisol, enhancing its negative impact on neuroplasticity and neuron health. The bottom half of the figure shows that antidepressant treatments, by raising levels of serotonin, and hence of BDNF, promote neuroplasticity and neuron health. BDNF: brain derived neurotrophic factor; GR: glucocorticoid receptor. Up-arrows ↑ indicate an increase; down-arrows ↓ indicate a decrease.

Understanding depression and anxiety

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The diagram summarises the influences on neuroplasticity and neuron health that occur through their effects on BDNF and cortisol levels, and thus binding of these molecules to their respective receptors on brain neurons. It also lists factors that exert deleterious effects on neuroplasticity and neuron health via mechanisms that do not involve BDNF or cortisol. These are: adverse genetic and developmental factors, chronic depression or illness, and poor blood supply to the brain.

4.7 Antidepressants, BDNF levels and neurogenesis in the hippocampus