Alzheimer's disease is a brain disorder that gradually destroys neurons. Over 4.5 million people in America suffer from Alzheimer's, which mostly occurs in older adults. The risk of developing Alzheimer's disease approximately doubles every five years after age 65 and reaches to 50 percent by age 85. Patients afflicted with Alzheimer's disease lose their ability to learn, remember, reason, make decisions, communicate and carry out daily activities. The direct and indirect cost of caring for Alzheimer's disease patients has increased to at least $100 billion annually.
Stroke and traumatic brain injury can also cause neuronal loss and lead to cognitive decline.
The stimulation of neurogenesis may also be useful in treating depression. Depression is categorized by extreme changes in mood which may also be associated with psychoses. The association between depression, stress, and neurogenesis arose first from MRI imaging studies suggesting a reduction in right and left hippocampal volumes in major depression (Sheline et al., 1996; Bremner et al., 2000; Mervaala et al., 2000). Further research indicated that the volume loss in the brain seen in patients with depression was due to glucocorticoid-induced neuron loss specific to hippocampus (Lee et al., 2002 review; Lucassen et al., 2001; Sapolsky 2000).
Other studies further confirmed the close correlation between neurogenesis and depression. Data showed that chronic stress could cause both volume changes and reduction in neurogenesis (Czeh et al., 2001; Pham et al., 2003). On the other hand, agents that cause a reduction in neurogenesis also appear as causative agents in depression specifically glucocorticoids and depletion of serotonin (Brezun and Daszuta, 1999). Finally, research using X-rays to ablate new cells caused by fluoxetine-induced neurogenesis in mice could reverse the antidepressant behavioral activity in the novelty suppressed feeding paradigm (Santerelli et al., 2003).
One challenge for using neurogenesis to treat Alzheimer's disease or depression is that nascent neurons must still survive long enough to produce functional neurons. There exists a need for a neurogenic agent that promotes the proliferation of a neuronal precursor and that causes the differentiation and survival of the neurons.