Chapter 18 - Chapter 18 Drug Abuse Background Humans...

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Chapter 18 Drug Abuse
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Background Humans discovered long ago that many substances in nature (e.g. plants materials) had medicinal qualities Some of these also served as “recreational” drugs, or substances that produced pleasing effects (most notable example is alcohol)
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Addictive drugs Drug Sites of Action Ethyl alcohol NMDA receptor ANT; GABA A receptor ANT Barbiturates GABA A receptor AGO Benzodiazepines (tranquil) GABA A receptor AGO Cannabis CB1 cannabinoid receptor AGO Nicotine Nicotinic Ach receptor AGO Opiates t and t receptor AGO PCP and ketamine NMDA receptor ANT Cocaine Blocks reuptake of DA, 5-HT and NE Amphetamine Causes release of DA
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Physical vs Psychological Addiction Many people believe that “true” addiction is caused by the unpleasant side effects that occur when an addict tries to stop taking the drug Physical dependence vs. psychic dependence Heroin addiction considered prototype for all drug addictions: Heroin addicts become physically dependent on the drug Tolerance – decreased sensitivity to a drug that comes from its continued use Withdrawal – the appearance of symptoms opposite to those produced by a drug when the drug is no longer taken Tolerance may be produced by the body’s attempt to compensate for the unusual condition of heroin intoxication, thus when the addict stops taking the drug, the compensatory mechanisms will become apparent However, tolerance and withdrawal do not occur immediately, something else must be happening in order to get the addict to start taking the drug in the first place (i.e. reinforcing effects)
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Positive reinforcement Drugs that lad to dependency must first reinforce people’s behavior Positive reinforcement refers to the effect that certain stimuli have on the behaviors that preceded them Addictive drugs have reinforcing effects i.e. their effects include activation of the reinforcement mechanism Role in drug abuse The effectiveness of a reinforcing stimulus is greatest if it occurs immediately after a response occurs This phenomenon explains why the most addictive drugs are those that have immediate effects e.g. heroin is preferred over morphine because it has a more rapid effect The immediate reinforcing effects of a addictive drug can overpower the recognition of the long-term aversive effects
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Positive reinforcement Neural mechanisms All natural reinforcers cause the release of DA in the nucleus accumbens Addictive drugs (including amphetamine, cocaine, opiates, nicotine, alcohol, PCP, and cannabis) trigger the release of DA in the NA Some do this by increasing te activity of DA neurons in mesolimbic system Some inhibit reuptake of DA by terminal buttons
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Negative reinforcement A behavior that stops or reduces and aversive stimulus will be reinforced. This phenomenon is called negative reinforcment Do not confuse negative reinforcement with punishment For neg. reinforcement – the response must make an aversive stimulus
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This note was uploaded on 07/31/2011 for the course PSB 3004 taught by Professor Williams during the Spring '08 term at University of Florida.

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Chapter 18 - Chapter 18 Drug Abuse Background Humans...

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