Probiotic-based shot for stress, depression in the offing

A new probiotic-based immunisation treatment to protect against post-traumatic stress disorder (PTSD), anxiety, and depression may be on the horizon, scientists say.

According to researchers at the University of Colorado Boulder in the US, immunisation with beneficial bacteria can have long-lasting anti-inflammatory effects on the brain, making it more resilient to the physical and behavioural effects of stress.

"We found that in rodents this particular bacterium, Mycobacterium vaccae, actually shifts the environment in the brain towards an anti-inflammatory state," said Matthew Frank, a senior research associate at University of Colorado Boulder.

"If you could do that in people, it could have broad implications for a number of neuroinflammatory diseases," said Frank.

Anxiety, PTSD and other stress-related mental disorders impact as many as one in four people in their lifetime.

Mounting research suggests that stress-induced brain inflammation can boost risk of such disorders, in part by impacting mood-influencing neurotransmitters like norepinephrine or dopamine.

"There is a robust literature that shows if you induce an inflammatory immune response in people, they quickly show signs of depression and anxiety," said Frank.

Research also suggests that trauma, illness or surgery can sensitise certain regions of the brain, setting up a hair-trigger inflammatory response to subsequent stressors which can lead to mood disorders and cognitive decline.

"We found that Mycobacterium vaccae blocked those sensitising effects of stress too, creating a lasting stress-resilient phenotype in the brain," Frank said.

For the study, published in the journal Brain, Behavior and Immunity, Frank and Christopher Lowry, an associate professor at University of Colorado Boulder, set out to find out what exactly M vaccae does in the brain.

Male rats injected with the bacterium three times, one week apart, had significantly higher levels of the anti-inflammatory protein interleukin-4 in the hippocampus - a brain region responsible for modulating cognitive function, anxiety and fear - eight days after the final injection.

After exposure to a stressor, the immunised animals also showed lower levels of a stress-induced protein, or alarmin, called HMGB1, believed to play a role in sensitising the brain to inflammation, and higher expression of CD200R1, a receptor key for keeping glial cells (the brain's immune cells) in an anti-inflammatory state.

The immunised rats, as in the first study, exhibited less anxious behaviour after stress.

"If you look at the field of probiotics generally, they have been shown to have strong effects in the domains of cognitive function, anxiety and fear," said Lowry.

"This paper helps make sense of that by suggesting that these beneficial microbes, or signals derived from these microbes, somehow make their way to the hippocampus, inducing an anti-inflammatory state," he said.