The gut-brain axis, a bidirectional signaling pathway between the gastrointestinal tract and the nervous system, plays key roles in human health. Key elements of this pathway are the tens of trillions of microbes that comprise the intestinal microbiota, the composition of which likely changes with age. A new study suggests that transplanting fecal microbiota from aged mice donors impairs cognitive function in younger mice recipients.

Aging is the collective physiological, functional, and mental changes that accrue in a biological organism over time. It is the primary risk factor for many chronic conditions, including cognitive decline. Changes in the gut related to reduced barrier function and microbiota composition play key roles in the aging process.

The authors of the study transplanted fecal microbes from aged mice into young (adult) mice. Then they subjected the young mice to a battery of spatial learning and memory tests involving mazes and escape tunnels.

They found that the young mice that received fecal microbial transplants from the aged mice showed marked deficits in spatial learning and memory capacity. These changes were mediated via altered expression of proteins involved in maintaining neuroplasticity and neurotransmission in the hippocampus – a region of the brain involved in learning and memory. The transplantation did not induce deficits in locomotion or induce anxiety-like behaviors, common features in older mice.

• Link to full study.