CHICAGO, May 20 (Xinhua) -- The type of bacteria living in the gut can influence the development of Alzheimer's disease symptoms in mice, according to a study posted on the website of the University of Chicago (UChicago) on Monday.

By altering the gut microbiome, long-term antibiotic treatment reduces inflammation and slows the growth of amyloid plaques in the brains of male mice, though the same treatment has no effect on female animals.

In the study, researchers at the university examined the effects of antibiotics on a different mouse model of Alzheimer's disease known as APPS1-21. Long-term treatment with a cocktail of antibiotics reduced the formation of amyloid plaques in male mice but had no effect on females.

Antibiotic treatment also appeared to alter the activation of microglia in male mice, changing them from a form that is thought to promote neurodegeneration to a form that helps to maintain a healthy brain.

To prove that these improvements in Alzheimer's symptoms were caused by alterations in the gut microbiome, the researchers transplanted fecal matter from untreated mice into antibiotic-treated animals. This procedure restored the gut microbiome and caused an increase in amyloid plaque formation and microglial activation.

As for why alterations in the gut microbiome only affect male mice, the researchers discovered that long-term antibiotic treatment changed the gut bacteria of male and female mice in different ways. The changes in the microbiome of female mice caused their immune systems to increase production of several proinflammatory factors that could influence the activation of microglia.

"Our study shows that antibiotic-mediated perturbations of the gut microbiome have selective, sex-specific influences on amyloid plaque formation and microglial activity in the brain," said Sangram Sisodia, director of the Center for Molecular Neurobiology at UChicago. "We now want to investigate whether these outcomes can be attributed to changes in any particular type of bacteria."

Alzheimer's patients exhibit changes in their gut microbiome. Previous study shows that gut bacteria may influence the development of these symptoms in rodents.

Alzheimer's disease is characterized by the formation of amyloid plaques and the activation of immune cells present in the brain known as microglia. These cells can help remove amyloid plaques, but their activation may also exacerbate the disease by causing neuroinflammation.

The study was published in the Journal of Experimental Medicine.