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One of the big things the military has going on in research is in the area of stress resilience. I actually wrote up a proposal for prophylactic measures to foster resilience not too long ago - still don't know if that will ever get funded though. The idea is to find ways to bring about or amplify resilience to acute and/or chronic stress in military members. This has led to a wide array of ideas and plenty of research papers. Interestingly this has also sparked newer research into the physiological response to environmental stress itself. One recent publication in the Proceedings of the National Academy of Sciences is a good example.

The neuroscience research focused on neurogenesis in the hippocampus of rats - actually a specific portion of the hippocampus called the dentate gyrus. They found that neurogensis following a stressor led to persisting social avoidance behavior in the rats (a conditioned response) a month later. However, when the neurogenesis in the Dentate gyrus was inhibited following the stressor or "threat stimuli" as the paper utilized the subsequent behavior was lacking (not completely mind you but a significant difference). The idea on a simple level is that this neurogenesis corresponds to that stress event to promote avoidance - an ancient defense to keep an animal away from threats.

Okay, so why is this interesting? Well, neurogenesis in the DG has been usually found to be decreased by stress (Heine, Maslam, Zareno, Joels Y Lucassen, 2004) by the actions of hormones such as cortisol (Gould, Cameron, Daniels, Woolley & McEwen, 1992). Adult neurogenesis may also play a role in the behavioral aspects of depression (Sahay & Hen, 2007) but cannot be listed as a sole or large contributor to the etiology of the disorder. By contrast antidepressants usually increase neurogenesis (Malberg, Eisch, Nestler & Duman, 2000). The question here would be what role the surviving neuronal survival and the rate of neurogenesis play in the formation of conditioned stress responses such as avoidance.

Some research has found that epigenetic factors (in this case histone modification) may contribute to the complexities of stress response, conditioning and subsequent behavioral manifestations (by deduction) (Chandramohan, Droste & Reul, 2007). Similar research also found that the physiological changes induced by exercising changed the epigenetic influence outcome in relation to novel stress events - that is rats which were forced to exercise responded better to stress challenges than sedintary rats which corresponded to a higher number of specific neurons in the dentate gyrus which was due to the phospho-acetylation of histone H3 and c-Fos (transcription protein) induction (Collins et al., 2009)

Once we better understand the genetic, cellular and molecular processes, we can then better devise ways to inhibit the formation of stress related disorders such as acute stress disorder, PTSD and C-PTSD which are all major problems with deployed forces in hot zones across the globe.

References

Chandramohan, Y., Droste, S. & Reul, J. (2007). Novelty stress induces phospho-acetylation of histone H3 in rate dentate gyrus granule neurons through coincident signalling via the N-methyl-D-aspartate receptor and the glucocorticoid receptor: relevance for c-fos induction. Journal of Neurochemistry, 101, 815-828.

Collins, A., Hill, L., Chandramohan, Y., Whitcomb, D., Droste, S. & Reul, M. (2009). Exercise improves cognition responses to psychological stress through enhancement of epigenetic mechanisms and gene expression in the dentate gyrus. PLoS One, 4(1): e4330.

Gould, E., Cameron, H., Daniels, D., Woolley, C. & McEwen, B. (1992) Adrenal hormones suppress cell division in the adult rat dentate gyrus. Journal of Neuroscience, 12, 3642-3650.

Heine, V., Maslam, S., Zareno, J., Joels, M. Y Lucassen, P. (2004). Suppressed proliferation and apoptotic changes in the rate dentate gyrus after acute and chronic stress are reversible. European Journal of Neuroscience, 19, 131-144.

Malberg, J., Eisch, A., Nestler, E. & Duman, R. (2000). Chronic antidepressant treatment increases neurogenesis in adult rat hippocampus. Journal of Neuroscience, 15, 9104-9110.

Sahay, A. & Hen, R. (2007). Adult hippocampal neurogenesis in depression. Nature Neuroscience, 10, 1110-1115.

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In a different but equally interesting article (Grayson et al., 2010), researchers at Columbia university have managed to create a temporomandibular joint (part of the jaw) from adult stem cell cultures. Stem cells from embryonic lines have been previously utilized to induce bone growth (Jukes et al., 2008) but now it is possible that this can be done in approximately 5 weeks with adult stem cell lines - something that could avoid the controversy over the use of embryonic lines all together.

References

Grayson, W., Frohlich, M., Yeager, K., Bhumiratana, S., Chan, M., Cannizzaro, C. et al. (2010). Engineering anatomically shaped human bone grafts. Proceedings of the National Academy of Sciences, 107, 3299-3304.

Jukes, J., Both, S., Leusink, A., Sterk, L., van Blitterswijk, C. & Boer, J. (2008). Endochondral bone tissue engineering using embryonic stem cells. Proceedings of the National Academy of Sciences, 105, 6840-6845.