Your neurons also hibernate when you're sleep deprived

Like many, many people these days -- I am sleep deprived. I drag myself out of bed most mornings around 6 A.M. and keep going until I can't keep my eyes open anymore. I probably wouldn't make it though the day without at least 2-3 cups of coffee. Even so, the caffeine is merely acting as a physiological crutch and my brain is definitely not working at optimal capacity. My complaint is not new. If you've read this far, then I'm guessing 1) this isn't the first blog post you've read regarding this topic, and 2) you are probably familiar with the symptoms of sleep-deprivation already. Since this blog is about stem cells, I've been scanning a few papers to see how sleep deprivation may affect neural regeneration. I'm not trained as a neurobiologist, but now I find that subject to be truly fascinating.

During the past 30 years, neurobiologists have found that the brain can physically change in response to stressors and pleasures from daily life. Neurogenesis, or the birth of neurons, is responsible for some aspects of this remodeling. The generation and incorporations of new neurons is most closely connected with learning and memory, which means neurogenesis can occur throughout a lifetime. This also suggests that there's a resident pool of neural stem cells in the brain. However, it's not clear where these cells originate from or what specific properties they have - even though you'll find many reports of their discovery and characterization. It sounds paradoxical, but it's a common problem in the stem cell field. Nobody really knows what standards to apply, so nobody can claim they've found a real neural stem cell because they may be a partially differentiated cell and may just be an experimental artifact. The consensus criteria for calling something a "stem cells" are 1) the cell should be able to self-renewal, 2) the cell should be pluri-/multi-potent, and 3) the cell should be able to regenerate specific cell types. Yep, that's all. It's a very broad definition and doesn't cover possible grey areas. So when anyone claims to find some novel type of stem/progenitor cells (based on the above criteria) there's always someone else demanding more conclusive proof. But how does one prove something when there's no logical guidance for what would be acceptable as proof?

But I digress. As I was saying, the neurogenesis process can physically change the brain by supplying new neurons that are incorporated into the brain when I'm learning or making memories. Several papers have described the effects of sleep deprivation on neurogenesis^1-3. In short, stressors (such as sleep deprivation) reduce neurogenesis, which means there are fewer new neurons available and therefore fewer new connections can be made in the brain. That would help explain why I had to skim those papers several times before I understood the point they were making. Unfortunately, my reliance on caffeine doesn't help either. Studies have been conducted that showed caffeine actually depresses neurogenesis^4-5 and that's an unwelcomed revelation for me - I'm sipping a cup of coffee as I'm writing this post...

I really should just let common sense guide my actions if I want to keep my brain in tip-top shape. Sleep more, eat well, and exercise. They're activities we all know we're supposed to do. Yet, we don't make enough time for them. I wonder if I would need less sleep if I exercise more.

Photo credit: fugly.com (http://www.fugly.com/pictures/17379/sleep-deprivation.html)

References:

1. Mirescu C. et al. Sleep deprivation inhibits adult neurogenesis in the hippocampus by elevating glucocorticoids. Proc Natl Acad Sci U S A 103,19170-19175 (2006).
2. Junek A. et al. Short-term sleep deprivation may alter the dynamics of hippocampal cell proliferation in adult rats. Neuroscience 170,1140-1152 (2010).
3. Guzman-Marin R. et al. Hippocampal neurogenesis is reduced by sleep fragmentation in the adult rat. Neuroscience 148, 325-333 (2007).
4. Han M.E. et al. Inhibitory effects of caffeine on hippocampal neurogenesis and function. Biochem Biophys Res Commun 356, 976-980 (2007).
5. Wentz C.T. et al. Caffeine alters proliferation of neuronal precursors in the adult hippocampus. Neuropharmacology 56, 994-1000 (2009).