Brain-derived neurotrophic factor (BDNF) is exactly as it states; a neurotrophic factor usually derived in the brain. More specifically, it is a protein found in the neurons of the central nervous system that helps to support the survival of existing neurons, and encourage the growth of new neurons and synapses. It is active predominantly in the hippocampus, cortex, and basal forebrain—areas vital to learning, memory, and higher thinking.
Although the vast majority of neurons in the mammalian brain are formed prenatally, parts of the adult brain retain the ability to grow new neurons from neural stem cells; a process known as neurogenesis. Neurotrophins are chemicals that help to stimulate and control neurogenesis, BDNF being one of the most active.
Mice born without the ability to make BDNF suffer developmental defects in the brain and sensory nervous system, and usually die soon after birth, suggesting that BDNF plays an important role in normal neural development. Exposure to stress and the stress hormone corticosterone has been shown to decrease the expression of BDNF in rats, and leads to an eventual atrophy of the hippocampus if exposure is persistent. Similar atrophy has been shown to take place in humans suffering from long-term depression. On the other hand, voluntary exercise, caloric restriction, intellectual stimulation, and various treatments for depression (such as antidepressants and electroconvulsive therapy) strongly increase expression of BDNF in the brain, and have been shown to protect against this atrophy.
Various studies have shown possible links between low levels of BDNF and conditions such as depression, Obsessive-compulsive disorder, Alzheimer's disease, Huntington's disease, and dementia, though it is still not known whether these levels represent a cause or a symptom.
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