The Addictive Brain as taught by Professor Thad A. Polk Part III

Third in my series of the review of The Addictive Brain. Please see part one dated 12/5/2016 then part two dated 12/20/2015 if you haven’t read them yet. These 2 lectures cover alcohol and marijuana.

Lecture 7: Alcohol, Social Lubricant or Drug of Abuse?

The title makes the point that alcohol is regarded as a social lubricant. It’s legal, considered mandatory at most parties and many social functions and many people feel pressured to partake of alcohol in these social situations.

It turns out that alcohol behaves like many other drugs in that it binds to neurotransmitter sites and effects changes in their function. Alcohol binds to multiple sites to cause many different effects. One mentioned is that it binds to sites involved with learning and memory. This may explain why some people can “black out” drink and have no memory of what happened. There is also cross reactivity to the barbiturate class of drugs. People who have tolerance built up against barbiturates also have tolerance against alcohol. It takes them more drinks to get drunk. Another mechanism of tolerance is that alcohol induces your liver and GI tract to make more enzymes to break down the alcohol.

There are compensatory changes in the brain as a result of chronic alcohol exposure. Since alcohol is a depressant the brain compensates by becoming excitable. So with alcohol withdrawal you have excess excitability such as tremors and even seizures. Alcohol withdrawal is one of the most dangerous drug withdrawals. So alcohol behaves like a drug of abuse with respect to effecting neurotransmitters and in developing tolerance and withdrawal symptoms when withheld.

Now lets look at its addictiveness. Alcohol causes dopamine release in the Nucleus Accumbens so the reward center is stimulated. It also is associated with triggers that produce craving similar to drugs of abuse. Genetic factors also play a role in susceptibility to addiction to alcohol.

Treating alcohol addiction. First, detox. Sometimes substitutes such as valium are prescribed. Next comes psychosocial methods like rehab or group participation. Some medications can help. Such as disulfiram, (Antabuse). This makes it very unpleasant to drink. Naltrexone inhibits pleasure response of alcohol and can be useful. Acamprosate is a drug that seems to blunt the effect of alcohol. Said to be as effective as naltrexone in aiding abstaining from alcohol.

Lecture 8: The Science of Marijuana

The psychoactive chemicals in marijuana are called cannabinoids. The main psychoactive compound, isolated in 1964 is called Delta-9-Tetrahydrocannibinol (THC). In 1988 scientists found cannabinoid receptors in the brain. 2 main types of receptors were found, CB1 and CB2. The CB1 receptors in the brain are the receptors that result in it’s effects. After finding the receptors scientists looked for the natural neurotransmitters that bind to these receptors. In 1992 they found anandamide and later some others. These are called endogenous cannabinoids or endocannibinoids, meaning they are produced from within. THC would then be considered an exogenous cannabinoid or exocannibinoid, meaning produced externally.

Two important characteristics about endocannibinoids is that they are not stored in neurons but made as needed. Almost all neurotransmitters are made and stored in neurons and released when needed. They other important characteristic is that they seem to function as retrograde messengers. In other words, the cannabinoid receptors are on the neuron that is behind it in the chain of neuronal signals. This functions in regulating the functions of the presynaptic cell. It can prevent the presynaptic neuron from over firing.

There is evidence that this plays a role in forgetting things. For instance if you parked your car in a certain spot today you need to forget where you parked it yesterday so it won’t interfere with finding the car today. Genetically engineered mice that lack cannabinoid receptors can be trained to find food in a certain spot but they can’t unlearn it if you start placing the food in a new spot. Hence they will starve until you put food in the old spot. This can lead to some benefits in people with PTSD who have intense memories of past events that interfere with their present life. Also some people with PTSD seem to have less than average amounts of anandamide. This can also explain why heavy marijuana users often report memory problems and may interfere with learning.

Cannabinoid receptors are found in multiple areas of the brain including the reward centers. Users report multiple effects. Euphoria, exhilaration, inability to control laughter and laughing at things that aren’t funny. Increased appetite is common. Many report enhanced visual and auditory perception. May feel relaxed or calm. Time perception can be affected. Sometimes it can cause anxiety and paranoia. Also disorganized thoughts and impulsive behavior.

Some medical uses include reducing nausea and increasing appetite. Useful in patients on chemotherapy for cancer or who have AIDS. Can be helpful in pain management, especially when other medications have failed. May inhibit certain types of tumors.

Marijuana is the most widely used illegal drug in the world. 17 Million americans have used marijuana in the past month and 3 million are daily users. Most start in adolescence. 1/3 high school students have tried marijuana. About 9% of people who have tried marijuana become addicted. For alcohol that number is 15% and for cocaine it’s about 17% so you can say marijuana is less addicting than those drugs. The worst offender was nicotine at 32%. Marijuana stimulates the reward center in the brain and can result in addiction similar to other drugs.

People who are addicted do have withdrawal symptoms such as irritability, intense craving, anxiety, depression and reduced appetite. Evidence of tolerance is less clear. Most regular users report that they don’t need more drug to get the same high as they had in the past.

Effects of long term use are controversial. Regular marijuana use is correlated with poor academic achievement. It’s unclear if this is because there are social factors that correlate with poor academic achievement and these social factors lead to marijuana use. There also seems to be a correlation with what’s called an amotivational syndrome. People who are passive and have low motivation for accomplishment or productivity. Again correlation may not necessarily mean causation. It just might be people who are poorly motivated may be the ones more likely to choose marijuana. There is another correlation with people who later use hard drugs but most researchers do not consider marijuana a gateway drug. It’s just people who chose one drug are more likely to choose other drugs.

Long term health effects are insignificant. People who smoke marijuana generally smoke much less than the average cigarette smoker so the lung damaging effect are less over time.

Treatment is mainly behavioral. Cognitive behavioral therapy, support groups etc are the mainstay of treatment.

The next two lectures will cover the “hard drugs”. The stimulants and opiates.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s