New York, Nov 22 (IANS): Common probiotics sold in supplements and yogurt can decrease stress-related behaviour and anxiety, suggests new research.

"Our study has shown that simple probiotics that we normally use to keep our digestive tract in sync, could be beneficial to reducing our stress levels as well," said Aaron Ericsson from University of Missouri in the US.

In a series of studies, researchers tested how zebrafish behaved after doses of Lactobacillus plantarum, a common bacteria found in yogurt and probiotic supplements. 

Studying how gut bacteria affect behaviour in zebrafish could lead to a better understanding of how probiotics may affect the central nervous system in humans.

"Zebrafish are an emerging model species for neurobehavioral studies and their use is well-established in drug-screening," Ericsson noted.

In their first experiment, scientists added the bacteria to certain tanks housing zebrafish; other tanks of zebrafish received no probiotics. 

Then, the researchers introduced environmental stressors to both groups, such as draining small amounts of water from the tank and overcrowding.

"Each day we introduced a different stressor -- tests that are validated by other researchers and cause higher anxiety among zebrafish," Elizabeth Bryda, Professor at College of Veterinary Medicine, University of Missouri. 

"These are common environmental stress patterns, such as isolation stress and temperature change, so it made the tests relevant to humans as well," Bryda added.

By analysing the gene pathways of both groups of fish, the research team found that zebrafish that were given the supplements showed a reduction in the metabolic mechanisms associated with stress.

"Essentially, bacteria in the gut altered the gene expression associated with stress- and anxiety-related pathways in the fish allowing for increased signaling of particular neurotransmitters," Daniel Davis from University of Missouri noted.

To test their theory further, the researchers measured the movements of fish in their tanks using sophisticated computer measuring and imaging tools. 

Previous studies of fish behaviour have found that fish that are stressed tend to spend more time at the bottom of their tanks. 

Once the fish were administered probiotics, they tended to spend more time toward the top of the tanks -- the change in behaviour indicating they were less stressed or less anxious, according to the findings published in the journal Scientific Reports.