Gut Bacteria and Cognitive Decline in Aging Mice
A certain type of gut bacteria that increases in numbers as mice age is linked to cognitive decline, according to a recent study. Researchers found that this bacterium affects communication through sensory nerves that connect to the brain.
While these experiments were conducted on mice, David Vauzour, a biochemist at the University of East Anglia in the UK, suggests that the gut-brain connection they found might also exist in humans. It’s still something that needs verification, but if true, this could help explain why memory and learning abilities seem to diminish as people get older. It might even point to potential gut-targeted treatments that could reverse this decline.
The bacterium appears to lower the efficiency of the gut-brain connection in mice, which resonates with other age-related changes. Christoph Thaiss, an immunologist at Stanford University, points out that, as we age, we often need aids like glasses or hearing devices. The study, published today in Nature, indicates that just as aging affects our sensing of the external world, it might also impair our recognition of internal signals.
Memory Testing
To study the role of gut microbes in aging, researchers placed young mice, about two months old, with older mice, around 18 months old. This can be likened to a teenager living with someone in their late 50s.
After a month in shared quarters, the younger mice started to show similar performance levels as the older ones on tasks involving mazes and memory. Typically, mice with good memories will explore new objects more than those they have seen before. However, the younger mice began spending equal amounts of time with both familiar and new objects, which mirrored the behavior of the older mice and indicated a loss of short-term memory.
Timothy Cox, a neuroscientist at the University of Pennsylvania, mentioned, “Their deficit was so profound, they were basically undistinguishable from the old mice. It was almost unbelievable.”
What changed was that the microbiomes of the young mice began to resemble those of the older mice. Due to their habits of living close together and consuming each other’s waste, they can easily exchange gut microbes. Researchers believed that certain bacterial species from the older mice were contributing to cognitive decline.
To investigate, they introduced various bacterial species to young mice, focusing on one specific type, Parabacteroides goldsteinii. When this bacterium was transplanted into young mice, it negatively affected their ability to remember previously encountered objects. Interestingly, when older mice were treated with antibiotics to eliminate their gut bacteria or a phage therapy targeting P. goldsteinii, their performance on the same memory task improved to levels comparable to those of young, healthy mice.
