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The brain link: researchers have discovered an amazing connection between how the brain is involved in obesity and drug addiction.

Lesson Plans for Student Activities

PREPARATION: Before beginning the lessons, make two photocopies for each student of Student Activity Reproducible 1 for a pre-test and post-text quiz (see the Assessment Guide below for more information) and one copy for each student of Student Activity Reproducible 2.

Lesson 1: Obesity and Drug Addiction--What Do You Know?

OBJECTIVE To give students information about the connection between drug addiction and obesity; to increase students' understanding of addiction and the brain; to broaden students' understanding of the scientific process; and to assess students' knowledge of the topics before and after reading the article


Life Science; Technology; Science in Personal and Social Perspective


* Before beginning the lesson, hold a class discussion based on these questions: "Are there more teens who have weight problems now than in the past?" "How big of a problem is obesity?" "Could there be a connection between obesity and drug addiction?"

* Tell students that they are going to find out how much they know about food addiction and its connection to drug abuse. Distribute copies of Student Activity Reproducible 1. Tell students to write their names on the paper and label it No. 1. Then have them answer the questions. Collect and grade the papers.

* Have students read the article, "Obesity and Drug Addiction: The Brain Link." Next, hold a discussion based on these questions: "What is the connection between obesity and drug addiction?" "How can this connection help scientists understand how to treat and prevent both conditions?"

* Next, tell students it's time to find out how much they've learned. Give them a second copy of Student Activity Reproducible 1. Tell them to write their names on the paper and label it No. 2. When students have finished, collect the papers, score them, and record your data in the Assessment Guide below.

* Wrap up the lesson by discussing the "chicken-and-egg" question from the article: "What comes first, obesity or drug addiction, or a low level of D2 receptors in the brain?"


1. d; 2. c; 3. c; 4. b; 5. d; 6. b; 7. c; 8. c; 9. d; 10. a.

Lesson 2: Dangerous Cravings and the Brain

OBJECTIVE Students use scientific data to draw conclusions about the effect of increasing D2 dopamine receptor levels in the brain.


Science as Inquiry; Science in Personal and Social Perspective


* Tell students that scientists know, that D2 receptor levels are lower in people who suffer from obesity or drug or alcohol addiction. Ask students why they believe this is so.

* Explain that students will read about an experiment in which alcohol-addicted and non-alcohol-addicted rats were medically altered to increase D2 receptor levels in their brains. The researchers compared the alcohol intake of the rats before and after the treatment. Ask students: "If increasing the D2 receptors causes the alcohol-addicted rats to stop drinking, what might be the implications for humans?"

* Distribute Student Activity Reproducible 2. Have students complete it.

* Wrap up the lesson by asking students to speculate on how this experiment and others like it might lead to useful treatments for addiction.


1. Yes, the increase in D2 receptors led to a drop in alcohol consumption. 2. Alcohol consumption fell in both groups, but the percentage drop was larger among the alcohol-addicted rats. In the non-alcohol-preferring rats, the D2 increase almost totally abolished alcohol consumption. In the rats that preferred alcohol, it reduced alcohol consumption to the level normally seen in non-alcohol-preferring rats. 3. This was done as a control to show that it wasn't the pressure of the needle itself but the D2 receptor gene causing the change in consumption.

Obesity and Drug Addiction--What Do You Know

Test your knowledge of obesity, drug addiction, and the possible connection between the two by taking this quiz. Circle the correct answer to each question.

1. Between 1980 and 2002, the proportion of overweight teens in the United States

a. didn't change.

b. doubled.

c. fell by half.

d. tripled.

2. What percentage of U.S. teens is at risk for becoming overweight or obese?

a. 5 percent

b. 10 percent

c. 15 percent

d. 20 percent

3. Which of the following health problems is not associated with obesity?

a. diabetes

b. arthritis

c. schizophrenia

d. heart disease

4. In what organ did researchers find similarities between obese people and people addicted to drugs?

a. stomach

b. brain

C. skin

d. lungs

5. Which natural chemical activates the brain's reward circuits?

a. insulin

b. norepinephrine

c. endorphins

d. dopamine

6. People addicted to drugs and obese people tend to have lower-than-normal numbers of

a. brain cells.

b. D2 receptors.

c. insulin receptors.

d. family members.

7. People addicted to drugs tend to have damage to a part of the brain responsible for judgment and impulse control. It is

a. the brain stem.

b. the hypothalamus.

c. the prefrontal cortex.

d. the cerebrum.

8. Teens with a body mass index (BMI) above the 95th percentile are considered

a. underweight.

b. normal weight.

c. overweight.

d. obese.

9. Which of these boosts the number of D2 receptors in the brain?

a. overeating

b. drinking alcohol

c. reading

d. exercise

10. If you think you are overweight, you should

a. check with your doctor.

b. buy a diet book.

c. diet immediately.

d. run 10 miles.

Dangerous Cravings and the Brain

Researchers have found that people suffering from obesity, alcohol addiction, and drug addiction tend to have lower-than-average numbers of D2 (dopamine) receptors in their brains. In 2001, researchers at Brookhaven National Laboratory in New York conducted an experiment using rats to find out if increasing the number of D2 receptors in rats' brains would decrease the amount of alcohol consumed by rats that had been trained to prefer alcohol over water. The experiment was conducted with two groups: normal rats and rats that had been trained to prefer alcohol.

Rats, D2 Receptors, and Alcohol Intake

Hypothesis: An increase in the number of D2 receptors in the brains of rats trained to prefer alcohol will make alcohol less appealing and cause them to drink less of it.

Brief Description of Experiment: The researchers, led by Panayotis K. Thanes, injected a virus carrying the D2 receptor gene into the nucleus accumbens (the pleasure center of the brain) of rats. This caused their brains to produce more D2 receptors. Brain imaging techniques were used to measure the increase. Of the 15 rats that received injections, six had been trained to prefer alcohol over water. (On average, 60 percent of the liquid they chose to drink was alcohol.) Nine rats preferred water. The experiment began when the needle that would carry the gene was implanted in the rats' brains as a control. After eight days with the needle in place, the virus-carrying gene was injected. Each day, scientists measured the rats' alcohol intake. The rats could choose from two bottles: one filled with water and the other with alcohol.

The Results of the Experiment


Alcohol intake over time for rats that preferred water and were injected with the D2 receptor gene on Day 8.


Alcohol intake over time for rats that preferred alcohol and were injected with the DR receptor gene on Day 8.

D2 Receptor Levels

In both alcohol-addicted and non-alcohol-addicted rats, D2 receptor levels rose--in most cases there was an approximate 50 percent increase about four days after injection of the virus-carrying gene. The D2 receptor level fell to about 8 percent above normal levels by the tenth day after the injection.

Now that you have read about the experiment, answer these questions. Write your answers on the back of this page.

1. Did the researchers prove their hypothesis?

2. Hew did the results differ in the alcohol-addicted and non-alcohol-addicted rats? Are the results permanent?

3. Why do you think researchers waited eight days before injecting the D2 receptor gene?

Ask experts to name the biggest health threats for teens today, and these two answers will rise to the top: obesity and drug addiction.

Are you surprised by the first answer? You shouldn't be.

More and more teens weigh far too much, and the problem is growing. It's no joke. Check out these numbers: 16 percent of young people between the ages of 12 and 19 are overweight, according to a 1999-2002 federal study by the Centers for Disease Control and Prevention. That's more than triple what the rate was between 1976 and 1980. The same study revealed that an additional 15 percent of teens are at risk of becoming overweight.

What's so bad about being overweight or obese? For starters, it can cause diabetes, a life-shortening disease in which the body loses its ability to metabolize sugar. It can also lead to asthma and can cause heart disease. Most obese people just aren't healthy, overall.


What do you think? Could the health threats of drug addiction and obesity be connected? If you're like most people, you probably think, "No way." Well, you--and most people--are wrong!

Think about it. People addicted to drugs and those who suffer from obesity have at least one thing in common. It can be extremely hard for them to stop doing things that they know are harming them. For the drug abuser, it's taking drugs. For the obese person, it's usually excessive eating (although there are other factors as well, as we'll learn). NIDA researchers decided to find out if and how the two disorders could be related. Their amazing new findings indicate that there is a link. If you think back to what you've learned from earlier articles in this series, you can probably guess what the link is. Got it? It's dopamine and the brain.

Researchers are discovering that obesity (like drug addiction) is, at least in part, a brain disease.


How did researchers find the obesity-addiction link? They started by reviewing what they already knew: Dopamine is a brain chemical that stimulates pleasurable feelings. When dopamine binds to special structures in your brain--called D2 receptors--it activates the brain's reward circuits. The end result? You feel good.

For some time now, researchers have known that people who are addicted to alcohol, cocaine, and other drugs tend to have a lower-than-average number of D2 receptors in their brains. That makes sense when you think about it. If you have a shortage of D2 receptors, it's harder for you to feel good. It's harder for dopamine to find a D2 receptor to bind to, so it takes more dopamine for you to feel pleasure. As it happens, most drugs of abuse cause a flood of dopamine in the brain. Taking drugs makes people feel better--in the immediate short term.

Researchers also knew that eating can stimulate the production of dopamine in the brain. Could it be that obese people suffer from a shortage of D2 receptors? They might need to overeat to get feelings of pleasure from food.

Using PET scanners to look inside the brains of obese and non-obese people, researchers Nora Volkow, M.D., who is now the director of NIDA, and Gene-Jack Wang, M.D., found that obese people do have lowered numbers of D2 receptors. In fact, Drs. Volkow and Wang's research at Brookhaven National Laboratory in New York showed that the more obese the person, the lower the number of D2 receptors. "The low number of receptors in obese people might be causing them to overeat," says Dr. Wang. "They might be doing it to compensate for reduced stimulation in their brain's reward circuits."

Dr. Volkow adds, "An individual who has low sensitivity to normal stimuli learns behaviors, such as abusing drugs or overeating, that will activate them."


Just because obese people and drug addicts share a shortage of D2 receptors, does that mean their disorders are caused by the lack of receptors? Not necessarily. It's a classic "chicken-and-egg" question. In other words, which comes first--the addictive behavior or the D2 shortage? Maybe the addictive behavior causes the shortage. Or ... maybe the shortage causes the behavior?

Dr. Wang says an experiment with animals indicates that "having plenty of D2 receptors does protect against drug abuse and obesity." So, that's some evidence that the D2 shortage causes the behavior. The experiment Dr. Wang is talking about worked like this: Panayotis K. Thanos, a Brookhaven National Laboratory researcher, trained rats to regularly take alcohol, then introduced additional D2 receptors into their brains. As soon as the receptors took hold, the rats' consumption of alcohol decreased. Dr. Wang says researchers have had similar findings involving cocaine and food.

Case closed? Not exactly. Scientists also know that the flood of dopamine in the brain that drug abuse causes can overstimulate the reward pathways--and cause a reduction in D2 receptors in abusers' brains. "In the end, people who become addicted could be much worse off biologically than when they started," says Joseph Frascella, Ph.D., of NIDA's Division of Treatment Research and Development.


Of course, there are major differences between drug addiction and obesity. For one, according to Dr. Wang, obesity is not all about the brain. "You have to consider a person's metabolism and other genetic issues," he says. "The brain chemistry is just part of the picture." Dr. Wang adds that it's not accurate to describe an obese person as a "food addict." Rather, one should say that overeating is an "addictive behavior."

Also, drug addiction seems to cause more wide-ranging brain damage than obesity. For example, in people who are addicted to drugs, the drop in D2 receptors is often accompanied by a loss in functioning of the prefrontal cortex--the part of the brain responsible for judgment and impulse control. "In obesity, we didn't see any problems in the prefrontal cortex," says Dr. Wang. This probably explains why obese people, though compulsive when it comes to eating, have more control over their behavior than drug abusers.


NIDA scientists have made amazing discoveries about the connection between drug addiction and obesity. Although these discoveries are fascinating, can they help people? Yes, definitely. This new information can help people addicted to drugs, obese people, and healthy teens who want to avoid drug addiction or obesity.

How? First, the research shows us that having a healthy supply of D2 receptors in the brain can help stave off addictive behaviors. So, anything that increases D2 levels could be a valuable weapon in the battle against drug abuse and obesity. With this in mind, NIDA researchers are looking to develop new medications.

But is there anything safe and available now that can boost the level of D2 receptors in your brain? "Yes!" says Dr. Wang. "Exercise has been found to increase dopamine release and to raise the number of dopamine receptors," he says. "This suggests that obese people might be able to boost their dopamine response through exercise instead of eating--which is just one more reason to exercise if you are trying to lose weight." He feels that exercise can be helpful for recovering addicts, as well.

Dr. Wang also notes that animal studies have revealed that group interactions can increase D2 receptor levels.

So, exercising and spending time with family and friends can help you keep your mind and body healthy--and help you avoid developing addictive behaviors.

That's all good to know. But according to Dr. Wang, perhaps the most important way the research can help is by giving people an understanding of their own behavior. It helps remove the mystery and stigma that surround addictive behaviors. "When you know the reason why," says Dr. Wang, "it makes everything much easier."

Cutting Edge

How Do You Design an Experiment?

By using their knowledge of addiction and how the brain works, Dr. Volkow and her colleagues had an idea: Maybe obese people have low numbers of D2 dopamine receptors in their brains--just like drug addicts. How did the researchers test their theory? They used the scientific method. The scientific method--which scientists in all disciplines have followed for hundreds of years--has four steps.

1. OBSERVE Researchers observed that D2 receptor levels are lower than normal in many drug abusers.

2. QUESTION Researchers raised the question of whether obese people, whose behavior can be described as "addictive," might also have low D2 levels.

3. PREDICT Researchers came up with a hypothesis: People suffering from obesity will have lower D2 levels than people whose weight is normal.

4. TEST Researchers took PET scans of obese adults to see how many D2 receptors they had.

The researchers validated the experiment by testing a control group--a similarly made up group of non-obese people. Accurate results from the obese group are only obtainable by looking at the results from the control group. The researchers also made sure the experiment was quantitative. In other words, they made exact measurements. (It wouldn't have been enough to say, "There were oodles of D2 receptors in that thin woman's brain.") Finally, the experiment was valid because it was set up in a way that was replicable--it could be repeated and tested by other scientists.

Wake-Up Call How Much Is Too Much?

What's the difference between being overweight and "just a bit chunky"? The Centers for Disease Control and Prevention has very strict definitions of weight-related terms. They're not based on how a person looks in jeans, they're calculated using height, weight, and--for people under 21--age and gender.

If you're worried that you have a weight problem, you should talk to a health professional. He or she will likely determine your body mass index (BMI) using this formula:

BMI = (Weight in Pounds) / ((Height in Inches) X (Height in Inches)) x 703

With your BMI and a specially made chart, the health professional can determine what percentile your BMI falls into. The percentile shows how your BMI compares with that of other teens of the same gender and age.

* MI value at or above the 95th percentile is considered overweight.

* BMI value between the 85th and 95th percentiles is considered at risk for becoming overweight.

* BMI value between the 6th and 84th percentiles is considered healthy.

* BMI value below the 6th percentile is considered underweight.

As you may have noticed, there is no "obese" category for teens. That's because, unlike adults, young people's bodies are growing and changing. Once you reach adulthood, your body levels off. But teens who are overweight not only face health problems, they are also at higher risk for becoming obese as adults.

As BMI increases in adults, so does risk of the following:

* premature death

* diabetes

* cardiovascular disease

* high blood pressure

* arthritis

* certain cancers

If it tarns out that you do have a weight problem, you and your parents can talk with your health professional about what actions you can take to improve your health.

Facts for Real Life

Q. Why is the number of overweight teens growing so rapidly?

A. Nobody knows for sure. It could be that today's teens are less physically active than those a generation ago. It may be that people are eating bigger portions of food than ever before. Dr. Volkow thinks one factor is the increasing ease with which people can get food today. Researchers are finding that there's a region of the brain--called the dorsal striatum--that is programmed to draw people to food even when they're not hungry. "This system was once very important for survival," says Dr. Volkow. "It was important to want food whenever you could get it, because you never knew when it was going to be around." In the contemporary United States, though, where there are fast-food outlets and convenience stores on every corner, "the system doesn't serve any purpose anymore," says Dr Volkow. Now, with food so easy to get, people who follow their brains' instructions to eat, eat, eat are not staving off starvation--they're growing overweight.

Obesity and Drug Addiction: Key Teen Health Issues

--A message from Dr. Nora D. Volkow, Director of NIDA

Dear Teacher:

As someone who sees adolescents every day, you are no doubt concerned that the number of teens battling health-threatening weight problems is growing. What you may not realize is that NIDA researchers are discovering fascinating connections between obesity and another key teen health issue: drug addiction.

Amazingly, drug abusers and those who suffer from obesity appear to have a similarity in brain chemistry that seems partly responsible for these compulsive behaviors.

The common link is the neurotransmitter dopamine, the brain chemical responsible for stimulating feelings of pleasure. This year's fourth and final installment of Heads Up discusses this link, as well as obesity research and treatment. Like all of the articles in the series this year, this one reinforces our understanding of addiction as a brain disease--a disease that can be treated, understood, and, most important, prevented.

Learning about the seemingly unlikely link between obesity and drug addiction will give students an intricate view of how science works. It will also teach them that researchers can never know for sure where the facts will lead them. NIDA-sponsored scientists started out doing work on drug addiction but soon found themselves researching obesity, as well.

Thank you for taking time to share the lessons of Heads Up with your students. You have helped set the stage for a healthier, smarter, and drug-free generation of young adults.


Nora D. Volkow, M.D.

Director of NIDA
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Title Annotation:Two Teen Health Dangers: Obesity & Drug Addiction
Publication:Junior Scholastic
Date:May 9, 2005
Previous Article:The Shuttle returns.
Next Article:All things equal?

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