Although the implications for neurogenesis are not yet definitive, research demonstrates that neurogenesis may play important roles in areas of learning and memory, the effects of stress, effect of environment and exercise, addiction, depression, effects of damage such as stroke, neurodegenerative diseases, and stem cell research. These are just preliminary research results and more research still needs to be done to apply these results to humans.
Stress: It was discovered that a single exposure to a stressful experience results in a decrease in proliferating cells in the dentate gyrus in marmoset monkeys. This implies that the production of granule neurons in adults may be inhibited by stress in other species such as humans. (Gould et al., 1998).
Learning and memory:Studies have found that mice with a lower population of adult dentate gyrus cells at the immature stage had a deficiency in forming robust, long-term spatial memories (Deng et al 2009). Adult-born neurons also contribute to long term potentiation in the dentate gyrus, a process that sustains learning and memory. This suggests that hippocampal neurons may play an important role in the formation of synaptic connections and the transient storage of memories in humans (Gould et al 1999)
Depression: It is suggested that stimulating hippocampal neurogenesis may provide new opportunities for treating depression and anxiety disorders (Santarelli et al., 2003). It was also demonstrated that certain antidepressants enhance neurogenesis in mice which suggests that this model may provide future applications for the treatment of depression in humans (Sayhay et al., 2007).
Exercise: Research shows that exercise increases the production of new neurons in the dentate gyrus as well as improving learning and memory functions in rats (Uda et al., 2006). Overall, moderate exercise was found to enhance learning and memory, improve executive function, counteract mental decline related to age and disease, and prevent against atrophy in the brain. Exercise also has neuroprotective qualities especially with respect to the reduction of brain injury and delaying certain neurodegenerative diseases. It also improves brain plasticity and has therapeutic qualities which are found to be helpful in alleviating depression (Cotman C. W. et al., 2007). More research still needs to be done to asses how exercise and neurogenesis might apply to humans.
Neurodegenerative Disease: Many neurodegenerative diseases show impairments in neurogenesis, including reductions in proliferation, migration, differentiation, maturation, survival, integration, and functionality. People with Parkinsons disease, Huntingtons Disease, and Alzheimer’s exhibit an impairment in neurogenesis which may contribute to cell loss and dysfunction (Phillips et al., 2006). Some studies detected an increase in neurogenesis in certain diseases; however, many of the cells produced were functionally abnormal. In the future, endogenous replacement of lost neurons may be further studied ( Phillips et al., 2006). More research still needs to be done to asses how neurogenesis can be applied to neurodegenerative diseases.
Neural Stem Cells: Animal models have used NSC’s to help alleviate symptoms in models of diseases such as Parkinson’s disease, Alzheimer’s disease, spinal cord injury, epileptic seizure, demyelinating diseases,stroke and multiple sclerosis. Their self- renewal properties, asymmetric cell division, ability to produce neural tissue, and their capacity to differentiate gives us insight into the potential uses of stem cells to be transplanted to repair missing cells. However, questions still remain concerning the exact location of stem cells, the ways in which to definitively identify neural stem cells and distinguish them from other stem cells, and the mechanisms deciding what type of cell a stem cell will become. There is hope that in the future the answers to these questions will provide information that will give neural stem cells therapeutic value (Gage 2000). However, more work needs to be done to understand the functional significance and how these techniques and procedures might be applied to humans.