Brainwashing - what is between a cigarette, appetite and body weight? / Yitzhak Farnes

Cigarette smoking is the number one cause of preventable deaths. But many smokers are reluctant to stop smoking due to the fear of gaining weight

Cigarette smoking is the number one cause of preventable deaths. But many smokers are reluctant to stop smoking due to the fear of gaining weight. Many attribute the weight gain after quitting smoking to the fact that we are looking for something to occupy our mouth instead of the cigarette. However, a new study proves that indeed smoking, and nicotine in particular, significantly affects the degree of appetite and body weight.

As readers of Scientific American Israel, I appreciate that you all know that the brain is made up of nerve cells, also called neurons. The neuron secretes molecules called neurotransmitters (or nerve messengers), which activate the target cells of that neuron. These target cells, which can be other nerve cells, muscle cells or gland cells, have receptors that bind the neurotransmitter and consequently cause electrical or biochemical activity in the target cell that bound the neurotransmitter. There are a considerable number of different transmitters and each transmitter can have several different receptors that cause different phenomena. One of the best known transmitters is acetylcholine. It is the first neurotransmitter to be discovered, and it is secreted by neurons that activate skeletal muscles and cells in the heart and gut, but it is also active in the brain. The receptors that bind acetylcholine are divided into two types, and the type we are interested in here are receptors that are activated not only by acetylcholine but also by nicotine (yes, the substance found in cigarettes), and are therefore called nicotinic receptors. The nicotinic receptors consist of five protein subunits and depending on the composition of the units, receptors with different properties are obtained that are activated or blocked by specific molecules. For example, the nicotinic receptor 4β3α (found in the area of ​​the brain known as the hypothalamus) is activated by a molecule called cytisine.

Indeed, it was found in animals that the administration of nicotine or cytisine caused a loss of weight and appetite. This finding led to the hypothesis that the nicotine in cigarettes is the cause of weight loss due to appetite suppression. But it was not known if nicotine works in the brain or in other places in the body and what is the mechanism of its action. In June 2011, an article was published in the prestigious journal Science discussing this issue. The study was done in mice. The researchers showed with the help of substances that specifically activate or inhibit the 4β3α nicotine receptor, that activation of the receptor causes weight loss, while its inhibition eliminates the slimming effect of nicotine. Moreover, inhibiting the activity of the receptor in the rest of the body but not in the brain, did not affect the weight of the mice, a sign that nicotine penetrates the brain and acts there on the 4β3α nicotinic receptors. One of the places in the brain where there is a high concentration of 4β3α receptors is the hypothalamus, where there are cells called POMC that are rich in 4β3α receptors. These cells activate a whole chain of reactions that affect appetite, food intake and glucose metabolism and the development of insulin resistance. It turns out that nicotine, by activating the 4β3α receptors in the POMC cells, activates the chain of reactions that causes appetite suppression. This finding is important because it enables the development of drugs that will activate the 4β3α receptors and cause appetite suppression, thus making it easier to quit smoking.

Another neurotransmitter found in the brain is called serotonin and it also activates its characteristic receptors on POMC cells whose activation causes appetite suppression, similar to nicotine. But serotonin, most likely, acts on different POMC cells than those on which nicotine acts. Hence, different mechanisms determine the appetite and therefore it is possible to regulate body weight by more than one mechanism. In the meantime, a recommendation for smokers: you should very well stop smoking and certainly you shouldn't smoke just to maintain your weight.

About the author:

Yitzhak Ferns is a professor in the Department of Neurobiology of the Hebrew University in Jerusalem, the founder of the Israeli Association for Neuroscience and the founder of Belmonte Youth Labs in Jerusalem.

for further reading:

Nicotine decreases food intake through activation of POMC neurons. Mineur et al. Science, Vol. 332 no. 6035, pages 1330-1332, 10 June 2011

Serotonin 2C Receptor Activates a Distinct Population of Arcuate Pro-opiomelanocortin Neurons via TRPC Channels, Sohn et al. Neuron, Vol 71, No 2, pages 488-497, August 2011.

A vaccine against nicotine is about to be approved by the authorities

As any smoker can tell, quitting is the relatively easy part. The hard part is to avoid "falling", from the urge to light a cigarette that arises weeks and even months after quitting, so to speak. The patches, gums, and all the other tricks you use to get through the first few months usually don't help against the urge that comes back later.

This is one of the reasons for the great excitement of those responsible for public health regarding the vaccine component against nicotine, which is currently in clinical trials. As with all vaccines, the ingredient NicVAX, produced by NABI Biopharmaceuticals, activates the body's immune system and stimulates it to create antibodies against a specific target - in this case, nicotine molecules. Since immune responses are usually acquired throughout life, the manufacturers claim that the ingredient could serve as a long-term smoking prevention aid.