Cocaine hits mice even harder with low glycine levels

Researchers from the University of Wisconsin have found that common gut bacteria can enhance the effects of cocaine in mice.

The study's findings were published in the journal Cell Host & Microbe's edition on November 1. Their research shows how cocaine use promotes the development of bacteria, which consume a substance called glycine necessary for healthy brain function.

Mice respond to drugs more strongly as glycine levels drop, and these responses include aberrant behaviors such as markedly increased motility and desire.

Additionally, the mice's sensitivity to cocaine returns to normal levels when glycine is added back into the system or when a genetically altered bacteria is used; this shows that this amino acid can function as a mediator of addiction-like behavior in animal models.

“I was interested in the gut-brain axis, and I found it very new and exciting,” says first author Santiago Cuesta a neuroscientist at the University of Wisconsin School of Medicine and Public Health.

Cuesta and colleagues discovered that cocaine activates the QseC protein, which promotes the growth of proteobacteria, like E. coli, in mice's guts. These glycine-fueled bacteria outcompete the healthy gut bacteria that already reside in our digestive systems, occupying most of the available resources.

“The gut bacteria are consuming all of the glycine and the levels are decreasing systemically and in the brain,” says senior author Vanessa Sperandio, a microbiologist from the University of Wisconsin School of Medicine and Public Health. “It seems changing glycine overall is impacting the glutamatergic synapses that make the animals more prone to develop addiction.”

“Usually, for neuroscience behaviors, people are not thinking about controlling the microbiota, and microbiota studies usually don't measure behaviors, but here we show they’re connected,” says Cuesta. “Our microbiome can actually modulate psychiatric or brain-related behaviors.”

“I think the bridging of these communities is what's going to move the field forward, advancing beyond correlations towards causations for the different types of psychiatric disorders,” says Sperandio.