Reading Susannah’s story in Brain on Fire got me really interested in ways that a person’s immune system can have an effect on their neurological and psychological status. One study I found, by Capecchi et al., was able to show a direct link between a problem in the immune system and obsessive compulsive grooming behavior in mice. This excessive grooming behavior was characterized by excessive grooming to the point of hair loss and lesion development.
Hair loss in Hox8b mice
Time spent grooming.
Mice with obsessive-compulsive grooming behaviors were found to have a Hoxb8 mutation. In the brain the only cells that would express this mutation are microglial cells. Microglia are basically the macrophages of the brain as they clean up debris and pathogens. Through a series of experiment Capecchi et al., found that mice with the Hox8b mutation had 15% less microglia than normal mice. As the microglial lineage often originates in the bone marrow mice with the mutant Hox8b were given a bone marrow from a “normal” mouse. Over the following months the mutant mice stopped the obsessive compulsive recovered from the hair loss and lesions. These results show strong evidence that the obsessive compulsive grooming behaviors are a result of microglial deficiencies in the brain.
I think that this is really interesting. A small deficiency, one mutation, can cause such harmful behavior. It makes me wonder what other disorders can be attributed to problems within the immune system.
Chen, Shau-Kwaun, Petr Tvrdik, Erik Peden, Scott Cho, Sen Wu, Gerald Spangrude, and Mario R. Capecchi. “Hematopoietic Origin of Pathological Grooming in Hoxb8 Mutant Mice.” Cell 141.5 (2010): 775-85. Print
On Psychology and Neuroscience 
Reblogged this on Mindocr’s Weblog.
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I think it’s really interesting that an immune mutation in the brain could lead to neurological issues of a seemingly unrelated topic, with a deficiency in microglia leading to obsessive-compulsive grooming behaviors. I wonder if other studies have examined whether mutations in the Hox8b gene in humans, or its equivalent, are linked to OCD, or related orders like trichotillomania (hair pulling disorder). There was a study that came out somewhat recently about the benefits of sleep, and how cerebrospinal fluid is pushed through the brain more rapidly, washing away harmful waste products and toxins (https://www.sciencenews.org/article/sleep-allows-brain-wash-out-junk). It’s widely known that sleep deprivation is bad for you, with long-term sleep deprivation associated with depression and ADD – maybe these are linked to the accumulation of waste products in a manner similar to how the development of obsessive-compulsive behaviors linked to a deficiency in microglia cells, which help to clean out the brain.
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