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Chapter 18

PSYC 211 Chapter 18

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McGill University
PSYC 211
Yogita Chudasama

Chapter 18 – drug abuse Common features of addiction Addiction – latin word addicere ‘to sentence’ in term of involuntary servitude, being obliged to fulfill the demands of his or her drug dependency. A little history Long ago, people discovered that the natural plants contains the medicinal characteristics, can reduce pain, prevent infections and also induces sleeping. They also discovered the ‘recreational drug’ = this gives the pleasurable effects when eaten, drunk or smoked. Table 18.1 addictive drugs Drug Sites of action Ethyl alcohol NMDA receptor (indirect antagonist), GABA receptor (indirect agonist) Barbiturates GABA receptor (indirect agonist) Benzodiazepines (tranquilizers) GABA receptor (indirect agonist) Cannabis (marijuana) CB1 cannabinoid receptor (agonist) Nicotine Nicotinic Ach receptor (agonist) Opiates (heroin, morphine, etc.) miu and sigma opiate receptor (agonist) Phencyclidine (PCP) and ketamine NMDA receptor (indirect antagonist) Cocaine Blocks reuptake of dopamine (and serotonin and norepinephrine) Amphetamine and Causes release of dopamine (by methamphetamine running dopamine transporters in reverse) Positive reinforcement – this refers to the effect the certain stimuli have on the behavior that preceded them. Additive drugs have reinforcing effects. Role in drug abuse – the most potent reinforcement occurs when drugs produce sudden changes in the activity of the reinforcement mechanism; slow changes are much less reinforcing. Neural mechanisms – addictive drug (amphetamine, cocaine, opiates, nicotine, alcohol, PCP and cannabis) trigger the release of dopamine in the nucleus accumbens, different drugs release the dopamine in different ways. Furthermore, the fact that the reinforcing properties of addictive drugs involve the same brain mechanisms as natural reinforcers indicated that these drugs ‘hijack’ brain mechanisms that normally help us adapt to our environment. It appears that addiction appears that the process of addiction begins in the mesolimbic dopaminergic system and then produces long-term changes in other brain regions that receive input from these neurons: • Ventral tegmental area changes, this is resulted from insertion of additional AMPA receptors into the postsynaptic of the DA neurons. • This leads to the increased activation in a variety of regions that receive dopaminergic input from the VTA: ventral striatum, NAC and the dorsal striaum, caudate nucles and putamen. • Synaptic changes that are responsible for the compulsive behaviors that characterize addiction occur only after continued use of an addictive drug. • The alterations that occur in the NAC and later in dorsal striatum include changes in dopamine receptors on the medium spiny neurons, further, increases are seen in dopamine D1 receptors, which cause excitation and faciliate behavior, and decreases are seen in dopamine D2 receptors, causes the inhibition and suppress behavior. Firstly, the potential addict experiences the pleasurable effects of the drug, reinforcing the behaviors that cause the drug to be delivered to the brain. Then, these behaviors become habitual, and the impulse to perform them becomes difficult to resist. The early reinforcing effects that take place in the ventral striatum encourage drug-taking behavior, but the changes that make the behaviors become habitual involve the dorsal striatum. One of the important feature of the dorsal striatum – automatic behavior, impaired for people with the parkinson’s disease. Negative reinforcement – the removal or reduction of an aversive stimulus that is contingent on a particular response, with an attendant increase in the frequency of that response. This often in the situation, where an individual is unhappy with his/her social status, a drug that reduces these feelings can reinforce drug-taking behavior by means of negative reinforcement. Craving – the urge of taking the drug to which one has become addicted. Commonly abused drug 1. Opiates – derived from a sticky resin produced by the opium poppy, it has been eaten and smoked for centuries. Addiction to this drug has several high personal and social costs. 1) Herion – type of opiates, has been criminal. 2). Tolerance, a person must take increasing amounts of the drug to achieve a ‘high’, since the drug is very expensive, and so the people spending a lot money on it, and become poor and then become a criminal for buying the drug. 3). Taking this drug by using unsanitary needle, and thus has a high chance of getting AIDS virus. 4). If the addict is a pregnant woman, her infant will also become dependent on the drug. 5). The uncertainty about the strength of a given bat
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