THE BURNED OVER DISTRICT

Everyone who has ever smoked marijuana has experienced the munchies, the hunger that occurs even if you have recently stuffed your face. Now researchers at Yale University have done the science and know why that is.

Horvath's group studies brain circuits that control hunger and satiety. In 2011, German researcher Marco Koch joined the lab to study how marijuana interferes with the body's ability to feel satiated.

Koch hypothesized that the active ingredients in pot turn off a set of neurons in the hypothalamus that play a central role in inhibiting hunger. Those neurons are known as POMCs.

Koch was surprised to find that instead of the POMCs being turned off in the mice, the neurons appeared to be turned on even more.

"It made no sense," Horvath said.

At first Horvath wasn't sure Koch had collected the data correctly, but after further analysis he concluded that the initial findings were right.

"And then we started to get excited," he said.

To see what was going on, the researchers used a technique that allowed them to artificially turn off the POMCs in the brains of the mice. When they gave the mice the chemical marijuana after turning off the POMCs, the mice ate less.

Next they artificially boosted the action of the POMCs, and the mice ate much more.

"The question became, how can it be that the same neuron that promotes satiety starts to promote hunger when it is exposed to cannibinoids?" Horvath said.

Further study revealed that cannibinoids, the active agent in marijuana, can change what kind of chemical the POMC neurons release. When a mouse is drug-free, its POMCs release MSH, a chemical that suppresses appetite. But when you give the same mouse marijuana, its POMCs start to release the opioid beta-endorphin, which promotes hunger.

"The whole circuitry turns upside down," Horvath said.

Marijuana will do that to you. I am surprised that they resorted to using mice. I would have thought there were more than enough stoners on campus for all the marijuana research they could imagine.