February 19, 2015
Why pot gives us the munchies
It’s long been known that smoking pot gives people the munchies, but what about marijuana causes this uncontrollable urge to consume mass quantities of junk food? That’s what a team of researchers from Yale University wanted to find out in a recently-published study.As the Los Angeles Times reported on Wednesday, Yale neurobiology professor Tamas Horvath and his colleagues got dozens of laboratory mice high on cannabis in an attempt to find out.
“Everyone knows that if you smoke dope after Thanksgiving dinner you will still go back and eat more – sometimes much more,” he told the newspaper. “We were interested to find out why.”
Blame appetite-suppressing neurons
Horvath’s team monitored the brain circuitry responsible for promoting eating by manipulating parts of the cellular pathway that governs marijuana’s action on the brain. They discovered that the munchies are actually caused by neurons typically responsible for suppressing appetite.
“By observing how the appetite center of the brain responds to marijuana, we were able to see what drives the hunger brought about by cannabis and how that same mechanism that normally turns off feeding becomes a driver of eating,” the professor said in a statement.
[Related story: Habitual marijuana use may increase brain abnormalities]
“It's like pressing a car's brakes and accelerating instead,” he added. “We were surprised to find that the neurons we thought were responsible for shutting down eating, were suddenly being activated and promoting hunger, even when you are full. It fools the brain's central feeding system.”
Prior research into the munchies
Previous research and anecdotal evidence have demonstrated that people under the influence of pot tend to continue eating long after they should have felt full, the Times said. Some scientists had hypothesized that the active ingredients of the substance switched off a set of neurons in the hypothalamus (known as POMCs) that play a key role in inhibiting hunger.
However, past experiments using stone laboratory mice has found the exact opposite appeared to be true – instead of POMCs being switched off in the mice, they become more active. The results “made no sense,” Horvath said, but analysis of the findings proved that they were correct.
[Related story: Skunk-like pot use linked to psychosis]
To investigate further, the Yale team used a technique that allowed them to artificially turn off the POMCs in the brains of the mice. When they gave the mice chemical marijuana afterwards, the mice ate less. Once they artificially boosted the action of those neurons, the creatures wound up eating far more.
Pot changes POMC release
As it turns out, the active ingredient of marijuana can actually change the type of chemical that the POMC neurons release. In drug-free mice, the POMCs release MSH, a chemical that acts as an appetite suppressant. However, when they are under the influence of pot, their POMCs start to release the hunger-promoting opioid beta-endorphin.
[Related story: Pot is bad for young people, but so is punishing them]
“This event is key to cannabinoid-receptor-driven eating,” said Horvath, who added that the behavior driven by these neurons is just one mode of cannabinoid receptor 1 (CB1R) signaling. More research is needed to validate the findings, as well as to determine if this mechanism is also involved in the process of getting high, he added.
The study was published in the latest edition of the journal Nature.