From: olivercranglejr@gmail.com   
      
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   On Friday, October 18, 2013 6:52:00 PM UTC-5, Oliver Crangle wrote:   
   > When Viruses Invade the Brain   
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   > Neurodegenerative diseases may result from a nasal infection   
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   > By Stephani Sutherland   
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   > Image: Patrick McDonogh/Getty Images   
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   > Neurodegenerative diseases were once considered disorders of the mind,   
   rooted in psychology. Now viruses rank among the environmental factors thought   
   to trigger brain-ravaging diseases such as multiple sclerosis (MS) and   
   Alzheimer’s disease. Human    
   herpesvirus-6 (HHV-6), in particular, has been linked to MS in past studies.   
   Neuroscientist Steven Jacobson and his colleagues at the National Institute of   
   Neurological Disorders and Stroke have determined that the virus makes its   
   entry to the human    
   brain through the olfactory pathway, right along with the odors wafting into   
   our nose.   
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   > The researchers tested samples of brain cells from people with MS and   
   healthy control subjects and found evidence of the virus in the olfactory bulb   
   in both groups. Infection via the nasal passage is probably quite common, as   
   is harboring a dormant    
   reservoir of HHV-6, but in people with MS, the virus is active. Genetics and   
   other unknown environmental factors probably determine the likelihood of the   
   virus reactivating once inside the brain, which can cause the disease to   
   progress.   
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   > The virus appears to invade the brain by infecting a type of glial cell   
   called olfactory ensheathing cells (OECs), which nourish smell-sensing neurons   
   and guide them from the olfactory bulb to their targets in the nervous system.   
   These targets include    
   the limbic system, a group of evolutionarily old structures deep in the brain,   
   “which is where viruses like to reactivate,” Jacobson explains. He points   
   out that olfactory neurons and their OECs are among the few brain cells known   
   to regenerate    
   throughout our life. This neurogenesis may keep our sense of smell sharp, but   
   at the cost of providing the virus the opportunity to spread.   
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   > This article was originally published with the title When Viruses Invade the   
   Brain.   
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   > To read the rest of this article, we recommend purchasing and downloading   
   the digital issue from a computer. Email this article link for reference.   
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   > http://www.scientificamerican.com/article.cfm?id=when-viruses-   
   nvade-the-brain&WT.mc_id=SA_CAT_HLTH_20120103   
      
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