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Cannabis exposure during adolescence may interfere with the brain’s maturation, at least in rats, according to research presented at the Society for Neuroscience meeting in San Diego this week. Scientists find that a synthetic cannabinoid can throw dopamine signaling out of whack and alter the development of the prefrontal cortex.

As states continue to legalize both medical and recreational marijuana, more and more teens are using the drug. According to the Scripps Research Institute’s Michael Taffe, who moderated a press conference today (November 6), 35 percent of high school seniors in the US have smoked pot in the past year, and 14 percent say they have smoked it every day for a month at some point in their lives.

This has cannabis researchers interested in how marijuana use affects teens’ developing brains. In one study described during the event with reporters, José Fuentealba Evans of the Pontificia Universidad Católica de Chile and his colleagues injected adolescent rats with a synthetic cannabinoid and found that such exposure had a “huge increase” in dopaminergic activity in the nigrostriatal pathway of the striatum compared with rats that received a placebo, he explains. This excitatory circuit plays a role in reward processing and addiction, for example, and such changes may encourage risky behavior.

In another study presented today, Jamie Roitman’s group at the University of Illinois at Chicago found that rats given this same drug had fewer inhibitory neurons in regions of the prefrontal cortex, as well as reduced levels of the perineuronal nets that help stabilize those circuits, compared with control animals. This part of the brain, which matures late in development as excitatory synapses are pruned and inhibitory synapses proliferate, controls the highly active motivational circuits, such as the nigrostriatal pathway, that mature earlier, Roitman explains.

“Adolescence is much more dopamine controlled, as you’re waiting for the prefrontal cortex to come online and execute planning and control over behavior,” she tells The Scientist. Thus, adolescents who use cannabis may be “at risk of changing the structure of the brain while it’s maturing.”