looks like , and how you quantify that ?
One way to look at fear is to quantify how often mice venture into wide open areas , which they normally avoid . If we give a mouse Valium or another anxiety-reducing drug , it will go out and explore and be carefree , not to say a bit reckless . Depression is often studied by looking at mice in a cylinder of water . They are good swimmers , but they don ’ t like swimming , so after a while , they ’ ll stop and adopt an immobile posture . Yet if you give them antidepressant drugs , they keep going .
These types of paradigms have shown their validity in studies of pharmacological agents used in human psychiatry , and so they ’ re ideal to explore whether microbiome manipulations have similar effects . This can be done by transplanting the microbes from a mouse model for a psychiatric disease to a healthy mouse to see whether that creates similar issues , or vice versa , to see if it can resolve them .
Following a similar logic , we have shown that the microbiome can be important in brain aging and cognitive decline . We took the microbiome from eight-week-old mice and gave it to 22-monthold animals — these are very old mice . And we were able to show wide-scale changes across the body — in the microbiome and the immune system , but also in the hippocampus , a brain structure involved in memory .
In the old animals that received the microbiome from young ones , the hippocampus looked completely rejuvenated in its chemical composition . They also performed significantly better in mazes designed to test their memory . This finding has now been replicated in two other labs , giving it further credence .
Such experiments are difficult if not impossible to do in people . How to make that jump ?
One thing we can do is to transplant microbes from the guts of people with psychiatric disorders to rodents , to see if they cause comparable behaviors . This has now been done for depression , anxiety , schizophrenia , social anxiety disorder and even Alzheimer ’ s disease . In one of our own studies , we transferred fecal microbiota from depressed patients to a rat model . This resulted in behavior reminiscent of that in rat models for depression , such as increased anxiety and an uninterest in rewards , in addition to inflammation .
In addition , we can see if bacterial strains we ’ ve identified as troublemakers in rodents also occur in people with psychiatric issues , and if strains that are beneficial in rodents can help humans as well .
What I ’ d really like to do is follow a large group of healthy people for a couple of years and track their mental and brain health as well as the changes in their microbiome , and regularly transplant their gut microbes into mice . This would give us a much better view on how this relationship evolves .
Do you think some of the probiotics available in stores today might be helpful , or not quite ? In my opinion , many so-called probiotics aren ’ t probiotics at all . Probiotics , per definition , are live microorganisms that , when taken in adequate amounts , can confer a health benefit . Most of what ’ s for sale in shops would never meet that criterion . To demonstrate that something confers a health benefit , you need clinical trials to show it is more effective than a placebo . That ’ s the first thing . Second , you have to show that the microbes are alive , and that they can survive the stomach acid .
There have been properly randomized controlled trials for some products . But for most products available over the counter today , such studies haven ’ t been done , because the regulatory
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The bland , “ beige ” foods served in many nursing homes may decrease the diversity and functioning of the residents ’ gut microbiomes , with potential negative impacts on brain health . CREDIT : PHANIE - SIPA PRESS / ALAMY STOCK PHOTO