Diet and microbiome may influence cognitive flexibility

There has been a lot of press recently about the microbiome’s impact on mood and behavior, the so-called ‘gut-brain axis’, and it appears now more than ever that the gut microbiome has a substantial impact on the brain.  A new paper out of Oregon State University, published in the journal Neuroscience, furthers this research by showing that different diets affect mice’s cognition and memory via changes in the microbiome.

Scientists fed groups of mice a normal chow and then switched their food to either high fat, or high diets, along with continuing some on the normal diet.   The researchers then put them through a battery of cognitive tests, all the while measuring their microbiomes using stool samples.  The mice on the high sucrose and high fat diets each had similar alterations of their microbiomes, such as an increase in Clostridiales and a decrease in Bacteroidales.  Mice on the high sucrose diet had decreased scores in their cognition tests, including memory and spatial reasoning tests, which corresponded to changes in the microbiome. For example, an increase in Lactobacilli was associated with a decrease in spatial reasoning.  Mice on the high fat diet, on the other hand, showed impaired working memory, which was associated with an increase in bacteroidales.

Some of these bacteria, such as Lactobacillus are used in probiotics to increase cognitive function, and there is some scientific basis for these effects, even though this study observes a somewhat different results.  The changes in this study though, were a diet intervention, which is more complex than a simple probiotic intervention.  That being said, we must remember that microbiome science is still developing, so each of these studies should be considered in the broader context of the field before any real conclusions can be made.

A recreational drug may cause memory loss due to the microbiome

There is a common method to induce schizophrenia-like symptoms in mice that is often used in research.  The method involves dosing the mice with a molecule called phenylcyclidine (PCP), better known as the drug angel dust.  There are neurological reasons why this drug should cause schizophrenia-like symptoms in mice, and one consequence of its administration is memory loss.  Researchers from Denmark recently tested if this memory loss was connected to the microbiome and published their results in Physiology and Behavior.

The researchers devised an experiment where groups of mice were either given PCP or a control.  All the mice had their microbiomes tested and underwent a memory test.  The scientists discovered that the PCP did heavily change the microbiome, with many genera increasing in abundance, like Roseburia, Dorea, and Odoribacter.  In addition, the memory performance also seemed to correlate with the microbiome.  As the microbiome rebounded after a 3 week time frame, so did the memory of the mice, even though some other symptoms of the PCP persisted.  Finally, the researchers gave some of the mice that were given PCP antibiotics so as to decrease the population of the microbiome.  The antibiotics were effective in restoring the memory of the mice even within 3 weeks, suggesting a microbiome connection.

The researchers hypothesize that stress caused from taking PCP may be the root cause of the microbiome shifts and memory loss.  Interestingly, some of the bacteria that they identified in the PCP microbiomes had been associated with stress in previous studies.  Here at the AMI we don’t like to preach to our readers, but if any of you use PCP and have a big exam coming up, you may want to consider stopping, or at least taking a probiotic.