Hunger and hormones determine food's appeal
(Medical Xpress) -- Its been said that there are two kinds of eating: eating to survive, or satisfy hunger, and eating for pleasure. The pathways in the brain that control each urge have been studied independently. But now, research by Howard Hughes Medical Institute investigator Jeffrey M. Friedman of Rockefeller University provides evidence that the two pathways are closely intertwined.
By activating regions of the brain linked to food-related pleasure, Friedman and colleagues discovered how the brain mediates the link between food preferences and hunger. Their findings were published online November 13, 2011, in the journal Nature Neuroscience.
Appetite based on hunger, Friedman discovered in the 1990s, is mediated in part by a hormone called leptin. When a mouse loses weight or is food-deprived, leptin levels fall, leading to an increase of food intake. Likewise, leptin levels rise in an animal after weight gain with a corresponding reduction of food intake. The available evidence further indicates that leptin plays the same role in humans.
Other researchers have shown that when people are eating, the brains so-called reward center is involved. Eating a food that tastes goodsuch as sugar is known to activate that areas dopamine (DA) neurons, which are also turned on by other pleasurable stimuli such as sex and cocaine.
Friedman and his colleague Ana Domingos suspected that changes in leptin concentration might affect these pathways in the brain and thus influence how much one likes food. The high reward value of sugar and other pleasurable foods presents an obvious challenge to dieters, and understanding leptins effects on eating for pleasure might suggest opportunities to intervene with potential therapies that reduce food cravings and diminish the risk of diet relapse, Domingos says.
Friedman and Domingos wanted to investigate these questions in mice. To do so, they needed to find a way to ask a mouse how much it liked sugar.
If I put a can of Coke, orange soda, or Diet Coke in front of you, you could taste them and tell me which you liked best, says Friedman. You cant do that with an animal.
So Friedman and Domingos collaborated with HHMI early career scientist Karl Deisseroth at Stanford University, who has developed a way to use a laser beam to turn on subsets of neurons at any time in the brain of a living mouse brain. Friedman and Domingos engineered mice so that DA neurons were activated when the laser was switched on by consuming liquids at a sipper, which tracks the number of licks an animal takes. By allowing the mice to control the activation of the DA neurons by licking, the researchers could get the mouse to like the associated drink. Then, they could determine whether that artificial activation of the reward pathway overpowered the reward signals the animal received from eating certain nutrients at a different sipper. Friedman and Domingos call the choice between self-induced activation of dopamine neurons or a sweetener such as sucrose an assay for liking.
With the system in place, the scientists exposed mice to different pairs of three different drinks: one with sucrosenatural table sugar; one with the artificial sweetener sucralose; and one with water. Normally, mice will prefer sucrose over sucralose and both sweeteners over water. But when the mice drank the water, the laser was switched on, activating their DA neurons and sending a reward signal to the animals brain. In the first choice between sucrose and laser, the mice still preferred sucrose to the water coupled to lasersuggesting that it naturally provides more reward than that conferred by direct activation of dopamine neurons. In contrast, the mice demonstrated no preference between water accompanied by the laser activation and sucralose.
When sucralose and sucrose are pitted against each other, mice choose the natural, calorie-containing sucrose the majority of the time. But when Friedman and his colleagues engineered the laser to turn on DA neurons when the mice drank sucralose, the mice began to prefer the artificial drink, sipping from the sucralose 84 percent of the time, indicating that the extra DA activation had shifted an animals preference from sucrose to sucralose.
Domingos says the findings help explain why, according to the US Department of Agriculture, natural sweeteners have consistently outsold artificial sweeteners ever since artificial sweeteners were introduced in 1947. This experiment shows that we prefer sugar to artificial sweeteners because of sugars actions in the brain, not only in the tongue. When we artificially add those actions to sucralose, then animals will like the artificial sweetener more, she says. To test whether levels of leptin affect hedonic reactions to sugar, Friedmans team repeated the experiments in mice that had been deprived of food for 24 hours. The hungry mice no longer preferred the combination of sucralose and DA activation to sucrose. Instead, they drank sucrose 93 percent of the time.
To determine whether the increased liking of sugar was really due to low leptin levels, the scientists next injected leptin into food-deprived mice. The animals once again preferred the sucralose and DA activation, drinking the artificial sweetener 69 percent of the time.
The switch in preferences, says Friedman, suggests that leptin levels affect how strong a role the DA system has in mediating food preferences. When an animal is food-deprived, with lower levels of leptin, the reward value of food with caloriessucroseis higher than that of sucralose accompanied by DA activation. Leptin reversed this effect: when the hormone was high, the animal liked sugar less, indicating its reward value had decreased. Friedman points out that further studies will be needed to determine how and where the nutrient value of sucrose is sensed.
Some people eat because theyre hungry, and other people eat because they like eating, says Friedman. And what this says is that in a sense theyre part of the same integrated pathway. This provides experimental evidence that -- similar to what we all know from our experience -- when youre hungry, you like food more. Having an assay to show this in animals provides an opportunity to further delineate these pathways.
Next, Friedman and Domingos plan to try activating smaller subsets of DA neurons to test which neurons are associated with sucrose and sucralose specifically. The experimental setup of combining neuron activation with food preferences can also answer other questions.
This is a new assay to measure how much an animal likes a particular nutrient, says Friedman. It can be applied to lots of other situationswe can now ask the same questions of fat or protein that we asked for sucrose and sucralose. Or test whether an animal has a liking for particular nutrients that it is deficient in.
Provided by Howard Hughes Medical Institute
- Brain's 'sixth sense' for calories discovered Mar 26, 2008 | not rated yet | 0
- Voluntary exercise by animals prevents weight gain, despite high-fat diet May 18, 2011 | not rated yet | 0
- Leptin-controlled gene can reverse diabetes Jan 05, 2010 | not rated yet | 0
- Sugar: Just how bad is it? May 04, 2011 | not rated yet | 0
- Sweet temptation: Brain signals amplify desire for sugary treats Jun 14, 2011 | not rated yet | 0
- Motion perception revisited: High Phi effect challenges established motion perception assumptions Apr 23, 2013 | 3 / 5 (2) | 2
- Anything you can do I can do better: Neuromolecular foundations of the superiority illusion (Update) Apr 02, 2013 | 4.5 / 5 (11) | 5
- The visual system as economist: Neural resource allocation in visual adaptation Mar 30, 2013 | 5 / 5 (2) | 9
- Separate lives: Neuronal and organismal lifespans decoupled Mar 27, 2013 | 4.9 / 5 (8) | 0
- Sizing things up: The evolutionary neurobiology of scale invariance Feb 28, 2013 | 4.8 / 5 (10) | 14
Pressure-volume curve: Elastic Recoil Pressure don't make sense
May 18, 2013 From pressure-volume curve of the lung and chest wall (attached photo), I don't understand why would the elastic recoil pressure of the lung is...
If you became brain-dead, would you want them to pull the plug?
May 17, 2013 I'd want the rest of me to stay alive. Sure it's a lousy way to live but it beats being all-the-way dead. Maybe if I make it 20 years they'll...
MRI bill question
May 15, 2013 Dear PFers, The hospital gave us a $12k bill for one MRI (head with contrast). The people I talked to at the hospital tell me that they do not...
Ratio of Hydrogen of Oxygen in Dessicated Animal Protein
May 13, 2013 As an experiment, for the past few months I've been consuming at least one portion of Jell-O or unflavored Knox gelatin per day. I'm 64, in very...
Alcohol and acetaminophen
May 13, 2013 Edit: sorry for the typo in the title , can't edit I looked around on google quite a bit and it's very hard to find precise information on the...
Marie Curie's leukemia
May 13, 2013 Does anyone know what might be the cause of Marie Curie's cancer
- More from Physics Forums - Medical Sciences
More news stories
For combat veterans suffering from post-traumatic stress disorder, 'fear circuitry' in the brain never rests
Chronic trauma can inflict lasting damage to brain regions associated with fear and anxiety. Previous imaging studies of people with post-traumatic stress disorder, or PTSD, have shown that these brain regions can over-or ...
Neuroscience May 18, 2013 | 5 / 5 (1) | 0 |
The neural machinery underlying our olfactory sense continues to be an enigma for neuroscience. A recent review in Neuron seeks to expand traditional ideas about how neurons in the olfactory bulb might encode information about ...
Neuroscience May 17, 2013 | 4 / 5 (1) | 0 |
(Medical Xpress)—What if the quality of your work depends more on your focus on the piano keys or canvas or laptop than your musical or painting or computing skills? If target users can be convinced, they ...
Neuroscience May 17, 2013 | 3.7 / 5 (3) | 0 |
Neurological disorders can have a devastating impact on the lives of sufferers and their families.
Neuroscience May 17, 2013 | 5 / 5 (1) | 0 |
If you're a left-brain thinker, chances are you use your right hand to hold your cell phone up to your right ear, according to a newly published study from Henry Ford Hospital in Detroit.
Neuroscience May 16, 2013 | 2 / 5 (2) | 0 |
Melbourne researchers have identified an immune protein that has the potential to stop or reverse the development of type 1 diabetes in its early stages, before insulin-producing cells have been destroyed.
56 minutes ago | 5 / 5 (1) | 0 |
When tumours metastasise, they can block lymphatic vessels, as researchers from ETH Zurich have discovered using a new method. The lymphatic fluid subsequently has to find a new path through the tissue. Such ...
10 seconds ago | not rated yet | 0 |
(Medical Xpress)—The feared Legionella pneumophila is responsible for legionellosis, an infectious disease that can lead to pneumonia. To infect humans, this pathogen has developed a complex method that allows it to camouflage ...
9 minutes ago | not rated yet | 0
Finnish researchers have shown that genetic marker information can improve risk evaluation of coronary heart disease. The study comprised over 24,000 Finnish subjects and was led by Professor Samuli Ripatti. The results revealed ...
6 minutes ago | not rated yet | 0
(Medical Xpress)—A powerful new way of imaging kidneys is providing scientists with insights into the importance of the body's filtering system and how it is affected by cardiovascular disease, stroke and ...
9 minutes ago | not rated yet | 0
A new study conducted using extensive medical records of over one million Israeli adolescents before military service shows clearly how exposure to the Israeli sun of young, light-skinned children increases substantially ...
8 minutes ago | not rated yet | 0