Link between gut bacteria and brain’s memory function

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Can probiotic bacteria play a role in how well your memory works? It’s too early to say for sure, but mouse studies have turned up some clues worth remembering.

Preliminary results suggest that giving mice the kinds of bacteria often found in dietary supplements have a beneficial effect on memory when it comes to navigating mazes or avoiding electrical shocks.

One such study, focusing on mazes and object-in-place recognition, was published last year. And researchers from the Pacific Northwest National Laboratory in Richland, Wash., are seeing similarly beneficial effects on memory in preliminary results from their experiments.

PNNL’s Janet Jansson provided an advance look at her team’s yet-to-be-published findings here today at the annual meeting of the American Association for the Advancement of Science.

The experiments gauged the effects of giving normal mice and germ-free mice a supplement of Lactobacillus bacteria — a type of bacteria that’s already been linked to improved cognitive function in patients with Alzheimer’s disease.

To measure how the presence of the bacteria affected memory, Jansson and her colleagues used a standard memory test that involved giving the mice a foot shock in a darkened part of the chamber, waiting several days, then seeing how well the mice knew to avoid the chamber’s dark place.

“The longer it takes for them to go back, the better memory they have,” Jansson explained.

She said the mice that were given the bacteria showed “much improved memory.”

The PNNL team then focused on the mechanism linking gut bacteria to brain function. The mice with the Lactobacillus boost showed elevated levels of mannitol, a sugar molecule that has some therapeutic applications.

And when the researchers looked at color-coded images of the hippocampus, a brain region that’s associated with memory, they found higher concentrations of GABA, a chemical that previous studies have linked to working-memory capacity.

“We’ve gotten some pieces of the puzzle, but it’s not complete yet,” Jansson said.

Joseph Petrosino, a microbiologist at Baylor College of Medicine, said that the link between Lactobacillus and memory improvement made sense, but that lots of details remain to be filled in.

“Lactobacillus is like the Swiss army knife of the microbiome. … The challenge is that, as with any microbial species, strain-to-strain variation can be as much as 40 percent,” Petrosino told GeekWire. “So not all strains are made equal. We have to understand which strains are doing what.”

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