There are many reasons that we divide drugs into classes. It's convenient to do so, and it helps provide some insight. For example, if we discover something about a given drug, then we need to consider it for other members of that class. If a successful treatment is discovered for a drug. Then it may apply to other members, of that class. Of course, these reasons may not hold for the last class of drugs, which is a catch all, and is made up of substances that may not fit everywhere else. That's the class of drugs called, others. Pending on the drug, the frequency of drug use can vary from a few percent in our survey to over 80%. Inhalants are just over 8%. Caffeine isn't even listed in this survey, but because it's found in so many different products, it's likely to be close to 100%. As we've seen, addicting drugs can be amazingly different. Some are legal while others are not. Some are stimulants, and some are depressants. Some improve function in some ways, and others don't. Some are gases, and some are solids. A few don't even produce a high. But all these drugs change the brain, so that there's a craving and repeated use in spite of negative consequences. Frequently, there are ad, additional serious toxicities, of theses drugs. These differences can be seen among the drugs that we've considered this week, inhalants, caffeine and the others. The inhalants are gases or fumes that get the user high. After prolonged use, they can produce almost a whole body toxicity. Caffeine is considered a mild stimulant that can become a problem for some. Drugs in the other class, can have many different toxicities, depending on the drug [SOUND] let's go over some of the basic ideas about drugs that we talked about, in previous weeks. First of all, drugs have to enter the brain to have an effect. The amount of drug that gets into the brain, is due to a balance among absorption, metabolism, and excretion. Remember that? Drugs act in existing systems in the brain. In this sense, the brain is a co-conspirator, in addiction. These existing systems are, except in rare cases, neurotransmitter systems. An example is cocaine. Which interacts with the neurotransmitter, dopamine. Cocaine blocks the transporter, and by doing so, increases dopamine levels in the synapse and at dopamine receptors. This initial molecular action, ultimately affects the neuronal circuitry in the brain. And the various brain regions, such that addiction eventually occurs. A key thing to remember about drugs is that, while they are very much like neurotransmitters, because they're active in the brain, they are also, very different. We can care neurotransmitters versus drugs. In neurotransmission, the duration of action of the neurotransmitter on the synapse and at receptors. It's very brief. It's just fractions of a second. But when it comes to drugs. They're in the brain for a long time, more like minutes and hours. The levels and distribution of neurotransmitters are controlled by brain mechanisms. On the other hand, the presence and distribution of drugs are determined by the drug user. It's a result of how much drug the user takes and how often, he or she takes it. Neurotransmission is a normal process. It's the basis of every thought, idea, and action that we have. But drugs distort this normal process. For example, the brain can remove neurotransmitters from the synapse very quickly. But the brain has no evolved mechanism for removing drugs from the synapse. For these reasons, drugs distort brain function. This distortion ultimately causes addiction, by mechanisms that we don't yet, fully and completely, understand. Another important factor about drugs that we discussed is that they can act at multiple receptor sites. Because different receptors are found in different brain regions, each drug can have multiple and different effects. This image shows how a molecule can bind to different sites. By presenting different aspects of its molecular shape. This particular image is just made up for purposes of conveying the idea, rather than being perfectly accurate. All of this information will hopefully help, put the drugs that we've discussed in perspective. Please examine the review questions at the end of this lecture, and be able to identify the naturally occurring neurotransmitter systems in the brain, that each class of drug acts through. Also, please be able to identify some of the major toxicities of each class of drug. For example, marijuana impairs functioning. Caffeine is a mild stimulant, but when taken in excess, it can elevate blood pressure, cause a tremor, and produce a nervousness, that can interfere with functioning.
