Interview with Dr. Bankole Johnson of the University of Virginia

Tailoring addiction medicine to fit the disease.

(The “Five-Question Interview” series.)

25 years ago, when Dr. Bankole Johnson first began giving lectures about addiction and neurotransmitters in the brain, he had a hard time getting a hearing. That’s because 25 years ago, everybody knew what addiction was: a lack of “moral willpower.” Or, at best, some sort of psychological “impulse control” disorder.  

As a neuropharmacologist by training, and currently professor and chairman of the University of Virginia’s Department of Psychiatry and Neurobehavioral Sciences, Dr. Johnson thought otherwise, and went on make a name for himself by discovering that topiramate, a seizure drug that boosts levels of the neurotransmitter GABA, could be used in the treatment of alcoholism. “I just wasn’t a hospital-type doctor,” he once said. “I was for more intersted in research than clinical practice.” Johnson’s work was featured in the 2007 HBO series, "Addiction."

Born in Nigeria, Dr. Johnson attended the University of Oxford and received his medical degree in Glasgow, Scotland in 1982. At the time, medical understanding of addiction was poor to nonexistent. “Everything we knew—really knew—probably could be written on the back of a postage stamp,” he recalled.

Since then, Dr. Johnson has published numerous articles on psychopharmacology and addiction, and has served on several National Institutes of Health committees and panels. (See my earlier POST on Johnson’s study of drugs for addiction in the American Journal of Psychiatry.)


1. You’re a native of Nigeria. How did you first become interested in medicine?

Bankole Johnson: My father was a doctor and encouraged me. Back then, I had little interest in medicine and was more interested in the arts and perhaps going to law School, for which I had been promised a scholarship.

2. Addiction is called a “disease of the brain,” in Alan Leshner’s famous phrase, but it is still a hugely controversial subject. Are innate biological differences the cause of addiction?

Johnson: Addiction is a brain disease. The roots of the disease lie in brain abnormalities, and these are exacerbated when a vulnerable person uses alcohol excessively or takes illicit drugs.

3. How did you discover that topiramate helped some alcoholics drink less?

Johnson: It was an idea that developed from a hypothesis I came up with based on brain neurochemistry. The central idea was to alter the signals of dopamine, a critical path for the expression of rewarding behavior, through two different and opposite systems—glutamate and GABA.

4. That work led to Topamax for alcoholism, and your more recent work with ondansetron, another GABA antagonist. But what role do environmental and sociocultural factors play in the development of addiction?

Johnson: The environment interacts with genes and brain chemistry to govern behavior. But in the end, it is the changes in the brain that ultimately direct alcohol and drug taking behavior.  The environment therefore provides the context and tuning of the neurochemical signals in the brain.

5. Some people find the notion of addiction as a progressive and incurable condition a hard pill to swallow, so to speak. Why has effective medical treatment for addiction been so slow to develop, and why hasn’t talk therapy been more effective?

Johnson: Talk therapy has some effectiveness, but alone it is not a comprehensive or robust treatment. Progress in the last two decades has been quite rapid. With growing and clear acceptance of the neurobiological underpinnings of addiction, the next decade should herald even more exciting discoveries.  For example, our work on pharmacogenetics promises to provide effective medications—such as ondansetron—that we can deliver to an individual likely to be a high responder, based on his or her genetic make up.

Photo Credit: Luca DiCecco

Reward and Punish: Say Hello to Dopamine’s Leetle Friend

  Dopamine recruits a helper to track drug rewards.

Ah, dopamine. Whenever it seems like researchers have finally gotten a bead on how that tricky molecule modulates pleasure and reward, and the role it plays in the process of drug and alcohol addiction, along come new findings that rearrange its role, deepening and complicating our understanding of brain function.

We know that the ultimate site of dopamine activity caused by drugs is the ventral tegmental area, or VTA, and an associated structure, the nucleus accumbens. But dopamine neurons in the VTA actually perform two distinct functions. They discriminate acutely between the expectation of reward, and the actual reward itself. Pavlov showed how these dual functions are linked, but the manner in which dopamine neurons computed and then dealt with the differences between expectation and reward—a controversial concept known as reward prediction error—was not well understood.

We all know about reward and punishment, however. Years ago, behaviorism’s emphasis on positive and negative reinforcement demonstrated the strong connection between reward, punishment, and learning. As Michael Bozarth wrote in “Pleasure Systems in the Brain,” addictive drugs “pharmacologically activate brain reward mechanisms involved in the control of normal behavior. Thus, addictive drugs may be used as tools to study brain mechanisms involved in normal motivational and reward processes.”

But how does the evolutionary pursuit of pleasure or avoidance of punishment that guarantees the survival of an organism—fighting, fleeing, feeding, and… fornicating, in the well-known “4-F” configuration—become a pathological reversal of this function? To begin with, as Bozarth writes, “the direct chemical activation of these reward pathways does not in itself represent any severe departure from the normal control reward systems exert over behavior…. Simple activation of brain reward systems does not constitute addiction!”

What does, then? Bozarth believes addiction results from “motivational toxicity,” defined as deterioration in the “ability of normal rewards to govern behavior.” In an impaired reward system, “natural” rewards don’t alter dopamine function as strongly as drug rewards. “Direct pharmacological activation of a reward system dominates the organism’s motivational hierarchy at the expense of other rewards that promote survival,” Bozarth writes. The result? Drug addicts who prefer, say, methamphetamine to food.

How does an addict’s mind become so addled that the next hit takes precedence over the next meal? A group of Harvard-based researchers, writing in Nature, thinks it may have a handle on how the brain calculates reward expectations, and how those calculations go awry in the case of heavy drug and alcohol use.

The dopamine system somehow calculates the results of both failed and fulfilled expectations of reward, and uses that data in future situations. Cellular biologists, with some exceptions, believe that dopamine neurons effectively signal some rather complicated discrepancies between expected and actual rewards. Dopaminergic neurons were, in effect, computing reward prediction error, according to the theory. They were encoding expectation, which spiked when the reward was better than expected, and fell when the reward was less than expected. As Scicurious wrote at her blog, Neurotic Physiology “If you can’t predict where and when you’re going to get food, shelter, or sex in response to specific stimuli, you’re going to be a very hungry, chilly and undersexed organism.” (See her excellent and very readable post on dopamine and reward prediction HERE. )

But nobody knew how this calculation was performed at the cellular level.

Enter research mice.

As it turns out, dopamine is not the whole story. (A single neurotransmitter rarely is.) Dopaminergic neurons account for only about 55-65% of total neurons on the VTA. The rest? Mostly neurons for GABA, the inhibitory transmitter. “Many addictive drugs inhibit VTA GABAergic neurons,” the researchers note, “which increases dopamine release (called disinhibition), a potential mechanism for reinforcing the effects of these drugs.” By inhibiting the inhibitor, so to speak, addictive drugs increase the dopamine buzz factor.

The researchers used two strains of genetically altered mice, one optimized for measuring dopamine, the other for measuring GABA. The scientists conditioned mice using odor cues, and offered four possible outcomes: big reward, small reward, nothing, or punishment (puff of air to the animal’s face). Throughout the conditioning and testing, the researchers recorded the activity of neurons in the ventral tegmental area. They found plenty of neurons with atypical firing patterns. These neurons, in response to reward-predicting odors, showed “persistent excitation” during the delay before the reward. Others showed “persistent inhibition” to reward-predicting odors.

It took a good deal of sorting out, and conclusions are still tentative, but eventually the investigators believed that VTA dopamine neurons managed to detect the discrepancy between expected and actual outcomes by recruiting GABA neurons to aid in the dendritic computation. This mechanism may play a critical role in optimal learning, the researchers argue.

Furthermore, the authors believe that “inhibition of GABAergic neurons by addictive drugs could lead to sustained reward prediction error even after the learned effects of drug intake are well established.” Because alcohol and other addictive drugs disrupt GABA levels in the brain’s reward circuitry, the mechanism for evaluating expectation and reward is compromised. GABA, dopamine’s partner in the enterprise, isn’t contributing properly. The ability to learn from experience and to accurately gauge the likelihood of reward, so famously compromised in active addiction, may be the result of this GABA disruption.

Naoshige Uchida, associate professor of molecular and cellular biology at Harvard, and one of the authors of the Nature paper, said in a press release that until now, “no one knew how these GABA neurons were involved in the reward and punishment cycle. What we believe is happening is that they are inhibiting the dopamine neurons, so the two are working together to make the reward error computation.” Apparently, the firing of dopamine neurons in the VTA signals an unexpected reward—but the firing of GABA neurons signals an expected reward. Working together, GABA neurons aid dopamine neurons in calculating reward prediction error.

In other words, if you inhibit GABA neurons through heavy drug use, you screw up a very intricate dopamine feedback loop. When faced with a reward prediction error, such as drug tolerance—a good example of reward not meeting expectations—addicts will continue taking the drug. This seems nonsensical. If the drug no longer works to produce pleasure like it used to do, then why continue to take it? It may be because dopamine-active brain circuits are no longer accurately computing reward prediction errors. Not even close. The research suggests that an addict’s brain no longer registers negative responses to drugs as reward errors. Instead, all that remains is the reinforcing signals from the dopamine neurons: Get more drugs.

[Tip of the hat to Eric Barker (@bakadesuyo) for bringing this study to my attention.]

Cohen, J., Haesler, S., Vong, L., Lowell, B., & Uchida, N. (2012). Neuron-type-specific signals for reward and punishment in the ventral tegmental area Nature DOI: 10.1038/nature10754

Photo Credit: http://www.zazzle.com