This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
For consumers of cannabis, passing the kouchie can often lead to the inability to pass up any munchies. A recent study conducted by a team of neuroscientists and led by Edgar Soria-Gómez and Giovanni Marsicano may shed some light on the marijuana-munchies connection.
Marsicano, principle investigator of a research group at the NeuroCentre Magendie in Bordeaux, France says, “It’s not that we found a new effect of marijuana.” He explains the study’s significance is its contribution to mapping out the brain’s mechanisms. “It’s very well known that marijuana increases hunger and it is also very well known to increase olfaction but we identified the circuits in the brain where this happens.”
It seems cannabinoids such as marijuana's active ingredient, tetrahydrocannabinol, or THC, contributes to a heightened sense of smell, which in turn may lead to an increased appetite. Their research indicates this happens, in mice at least, because THC fits into a cannabinoid receptor known as CB1 (for cannabinoid receptor type-1). They’re located in the brain’s olfactory bulb, which among many things, is the region of the brain that is responsible for sense of smell and controlling appetite.
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For the study, the researchers took two separate groups of mice--one group was given doses of THC and the other group was not. Then, they exposed both sets of mice to almond and banana oils to see how sensitive they were to their scent. (Incidentally, the banana and almond scented oils are not the equivalent of stoner mouse foods. They were used for technical reasons since the researchers needed something that had a food odor but wasn’t intrinsically associated with food. Banana and almond oils worked for this purpose since these mice hadn’t been exposed to them prior to the study.)
The researchers observed the mice--both sets of mice initially sniffed the oils; however, the non-THC dosed mice eventually lost interest while the ones dosed with THC continued sniffing and also ate much more chow, demonstrating an increased sensitivity to scent and an increased appetite.
They also repeated the same experiment with mice that had been genetically engineered without the cannabinoid receptor that THC binds to. Without the receptor, they found no difference between the mice who had been given THC and those that had not. Since the THC didn’t affect their appetite, it suggests that the munchies effect is dependent on the cannabinoid receptors in the olfactory bulb.
THC is an exogenous cannabinoid but natural cannabinoids, known as endocannabinoids, are also produced within the body. Marsicano explains how they send signals of hunger. “The scent of McDonald’s normally stinks to me,” he says. “But if I’m hungry and there is a McDonald’s maybe two blocks away, I smell it immediately and it smells beautiful. If it is 24 hours without eating, for example, I think the McDonald’s becomes stronger and more attractive. In this sense, our internal state, the hunger changes our perception to dictate our behavior. This is quite a common observation. In the paper, what we found is one of the mechanisms that is mediating this chain of events.”
As part of the study, the researchers looked at endocannabinoids in mice. They had the mice fast for 24 hours and found their olfactory bulbs began to produce endocannabinoids. Like the mice given THC, it resulted in an increased sensitivity to food scents and appetite, which may have occurred as a way to prevent starvation. If the mechanisms of THC are analogous to those of natural cannabinoids, it could be that THC-induced munchies may not only be caused by the ability to smell more acutely, it may also be that the desire to eat is due to sensations that are similar to food deprivation, meaning they may also occur because the brain has persuaded the body that it may be starving.
Image Credit: Commissioned by the study’s authors, this amazing art comes courtesy of Charlie Padgett