Psych 12 - Drug Addiction and the Brains Reward Circuits...

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Drug Addiction and the Brain’s Reward Circuits (383-399) Drug addiction is a serious problem in most parts of the world. Pharmacological (pertaining to the scientific study of drugs) principles and concepts, compares the effects of five common addictive drugs, and reviews the research on the neural mechanisms of addiction. Most laws governing drug abuse in various parts of the world were enacted before there was any scientific research on the drugs. Basic Principles of Drug Action Psychoactive drugs are drugs that influence subjective experience and behaviour by acting on the nervous system. The oral route of ingestion is the preferred route of administration for many drugs. Once they are swallowed drugs dissolve in the fluids of the stomach and are carried to the intestine, where they are absorbed into the bloodstream. Some drugs readily pass through the stomach wall, and these take effect sooner because they do not have to reach the intestine to be absorbed. Drugs that are not readily absorbed from the digestive tract or that are broken down into inactive metabolites before they can be absorbed must be taken by some other route. This route has advantages in that it is easy and relatively safe; its disadvantage is its unpredictability. Absorption from the digestive tract into the bloodstream can be greatly influenced by such difficult to gauge factors as the amount and type of food in the stomach. Drug injection is common in medical practice because the effects of injected drugs are strong, fast, and predictable. Drugs injections are typically made subcutaneously into the fatty tissue just beneath the skin, intramuscularly into the large muscles, or intravenously directly into veins at points were they run just beneath the skin. Many users prefer the intravenous route because the bloodstream delivers the drug directly to the brain. The speed and directness of this route leave little opportunity to counteract the effects of an overdose, an impurity, or an allergic reaction. Scar tissue, infections, and collapsed veins often form. Some drugs can be absorbed into the bloodstream through the rich network of capillaries in the lungs. Many anesthetics are typically administered by inhalation, as are tobacco and marijuana. It is difficult to precisely regulate the dose of inhaled drugs and many substances damage the lungs if they are inhaled chronically. Some drugs can be administered through the mucous membranes of the nose, mouth, and rectum. Once a drug enters the bloodstream, it is carried in the blood to the blood vessels of the CNS, the blood-brain barrier makes it difficult for many potentially dangerous blood-borne chemicals to pass from the blood vessels of the CNS to its neurons. Some drugs act diffusely on neural membranes throughout the CNS. Others act in a more specific
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This note was uploaded on 02/09/2012 for the course PSYCH 2220 taught by Professor Culham during the Spring '11 term at UWO.

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Psych 12 - Drug Addiction and the Brains Reward Circuits...

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