While some people experience a fun, euphoric high when smoking marijuana, others feel paranoid and anxious. Exactly why marijuana affects people differently has been poorly understood, but a new study published in Scientific Reports suggests one part of the brain may be responsible – at least, in rats.
"Until now, it was unknown which specific regions of the brain were responsible for these highly divergent effects of marijuana," said study author Steven Laviolette, a professor at Western's Schulich School of Medicine & Dentistry, in a statement. In a lab setting, researchers identified a target region in the brains of rats that Laviolette says “seem to independently control the rewarding, addictive properties of marijuana versus the negative psychiatric side-effects associated with its use."
Receptors for tetrahydrocannabinol (THC), marijuana’s psychoactive component, are found throughout the brain but exactly where the chemical interacts within the brain determines how one experiences it. Researchers microinfused rats with THC and recorded their behavioral responses and electrical responses in a part of the brain known as the nucleus accumbens, a complex frontal region responsible for reward behavior. This region in particular involves two neurotransmitters: dopamine (desire) and serotonin (satiety and inhibition). When THC responds to this region of the brain, it produces highly rewarding effects and enhances addictive behaviors in a way that is similar to opioid drugs like morphine. The nucleus accumbens is also involved in aversion processing in order to perceive potential threats, as well as helping to process what stimulates us, what we become addicted to, and reinforce reward behavior. When THC interacts in the posterior area of the nucleaus accumbens, researchers reported adverse cognitive and emotional symptoms similar to those found in people with schizophrenia.
In short, when THC interacts with the frontal region of the nucleus accumbens, the brains in rats were associated with a fun high. In the back, not so much. Of course, the study is just in rats, but the researchers note that it could help inform how and why certain people respond differently to the effects of marijuana.
"These findings are important because they suggest why some people have a very positive experience with marijuana when others have a very negative experience," said co-author Christopher Norris. "Our data indicate that because the reward and aversion are produced by anatomically distinct areas, the different effects between individuals is likely due to genetic variation leading to differential sensitivity of each area."
In other words, whether you enjoy getting high or not could literally be made in your DNA.