If there is one thing marijuana enthusiasts are known for, it’s packing away junk food like starving chipmunks. Just ask thirteen-year-old San Francisco Girl Scout Danielle Lei, who sold 117 boxes of cookies in under two hours this week by setting her stand up outside a dispensary. The increased appetite resulting from marijuana use is colloquially known as “the munchies,” and was the focus of a 2014 neuroscience study published in Nature.
The study was able to illuminate the mechanism by which the active compound in marijuana affects hunger and by doing so, to shed light on the complex neurological phenomenon of appetite.
The mechanisms underlying hunger are complicated and not fully understood. They involve a number of interconnected signaling pathways in the brain, which utilize transmitter molecules like dopamine and serotonin. These transmitters are released by neurons in the brain and then bind to specific receptors on neighboring neurons. Once bound, they alter how the neuron processes information and thus how that neuron’s owner thinks or feels.
Drugs like marijuana clearly affect how people feel, which means that they are in some way interacting with these same signaling pathways. University of Wyoming neuroscience professor Dr. Francis Flynn was able to offer his insight into how this is possible.
“The logic is that if it’s having an effect, it must be one mimicking a naturally occurring substance or transmitter in the brain,” explained Flynn. “And it must then be binding to a receptor in the brain that is naturally geared-up to bind that substance.”
“So with cannabis, that natural substance is endocannabinoids,” Flynn concluded.
The psychoactive component in marijuana is tetrahydrocannabinol, or THC. As one might surmise from the name, THC is a member of the cannabinoid chemical family. Members of this family – called endocannabinoids – occur naturally in the human brain as neurotransmitters.
“We now know that there are very specific receptors for these endocannabinoids, called CB1 and CB2,” said Flynn. “These cannabinoid receptors are the most prevalent receptor in the brain. So when you think about marijuana’s impact on brain function, it’s going to be incredibly wide-spread.”
These diverse affects appear to extend to appetite – THC is somehow able to alter how people perceive food.
“When we think about the rewarding properties of food,” said Flynn, “we say things like ‘it’s really good, it’s palatable, I love it’ – that pathway in the brain also has cannabinoid receptors.”
According to the paper in Nature, CB1 receptors are present in the portion of the mammalian brain called the olfactory bulb. This portion of the brain processes scents and contributes to the perception of tastes.
The scientists from the Nature paper were able to genetically engineer mice to lack CB1 receptors in the olfactory bulb. The researchers then dosed the genetically engineered mice with THC and allowed them to feast. What they found was that lacking a CB1 receptor led to decreased consumption compared to normal mice who were similarly dosed.
The conclusion drawn is that THC is able to affect cells in the olfactory bulb by binding to CB1 receptors. Once bound, THC induces some form of temporary neurological change that increases appetite.
At a glance, pumping mice full of psychoactive compounds doesn’t appear to have much of a practical application. However, the reality is starkly different; gaining insight into the pathways that control hunger could be incredibly important.
“Obesity is the number one enemy right now because of increased prevalence,” explained Flynn. “It’s linked with diabetes. It’s linked with hypertension. And also obesity is linked with progression of Alzheimer’s disease and insulin resistance.”
“The thought being, ‘Can we use drugs that may block the effects of these endocannabinoids? Could that be a way to control food intake?’” Flynn asked.
Understanding hunger could lead to treatments that address the obesity epidemic, as well as other appetite conditions like anorexia. THC is helping researchers investigate the endocannabinoid system, and in the process, tease out details about how the brain processes appetite. As for the laboratory mice, there are certainly worse gigs out there.
