What's the News: Scientists---and smokers---have long known that nicotine is an appetite suppressant, but just how it kept hunger at bay remained unclear. Now, researchers have uncovered the neural pathway by which nicotine reduces appetite, in a study published today in Science. This discovery could lead to new drugs that help people quit smoking or lose weight. How the Heck:

The researchers first observed that mice given nicotine or the drug cytisine, which binds to some nicotinic receptors in the brain, ate less and had less body fat than mice not given either drug. When the researchers gave mice a chemical compound that blocked nicotine receptors, the appetite-suppressing effects of these drugs went away.

Since cytisine binds particularly well to a type of nicotinic receptor called α3β4, the researchers figured that receptor might be the major player in decreasing appetite. Sure enough, when the researchers genetically knocked out that receptor in some mice, those mice were immune to the drugs' appetite-reducing effects.

The researchers then looked at what parts of the brain had α3β4 receptors, since different nicotinic receptors are present in different groups of neurons. These particular receptors show up in POMC cells, they found. This makes sense, given POMC cells are clustered in the hypothalamus---an area of the brain that plays a role in controlling lots of basic functions, including appetite.

What's the Context:

Since smoking tamps down appetite, many smokers gain weight when they stop---a common reason people hesitate to quit.

Importantly, these results show that nicotine causes a dip in appetite by a different pathway than it triggers addiction. This means that it's possible to make a drug that isn't addictive, but still has nicotine's appetite-suppressing powers.

Drugs that work on this POMC pathway could help smokers keep the weight off when they give up cigarettes, encouraging them to quit, and also be used to help non-smokers struggling with their weight.

Reference: Yann S. Mineur et al. "Nicotine Decreases Food Intake Through Activation of POMC Neurons." Science, June 10, 2011. DOI:10.1126/science.1201889

Image: Flickr / julianrod