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Dependence, Addiction, and the Self-Administration of Drugs. Ryan Webber. Explaining Drug Self-Administration . Try to use scientific theory to explain testable and reproducible theories on why drugs are abused Three Models: Disease model Dependence model
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Dependence, Addiction, and the Self-Administration of Drugs Ryan Webber
Explaining Drug Self-Administration • Try to use scientific theory to explain testable and reproducible theories on why drugs are abused • Three Models: • Disease model • Dependence model • Positive reinforcement model (learning)
Explaining Drug Self-Administration • Models not the same as theories, models are not mutually exclusive; if one is correct, the others are not necessarily wrong • All try to explain • Why behavior of drug addicts appears to be different from normal behavior • Why there are considerable differences between individuals in the development of drug abuse
Disease Model • Addictive behavior not the same as normal behavior because it is compulsive (beyond an individual’s control) and can be sometimes self-destructive • Disease model suggest that these “abnormal” behaviors are caused by a disease state brought on by drug usage
Disease Model History • In mid-19th century, drug abusers were considered deficient in character, moral fiber, willpower, and/or self-control – sinners and criminals • For this reason, only priests and clerics treated abuse • American social reform movements in the late 1800’s changed drug abuse viewpoints • American Association for the Cure of Inebriates – “Inebriety is a disease” • Physicians widely prescribed laudanum (opium and alcohol) – felt that they should help stop abuse of the drug
Disease Model History • Model faded until 20th century when Alcoholics Anonymous became popular – core tenet is that “alcoholism is a disease and that alcoholics cannot control their drinking and cannot be held responsible for their excessive intake and its effects” • DSM-IV does not use the term disease, but is a disorder – classifies it as a clinically significant psychological syndrome or pattern that is associated with present distress or disability
Strengths / Problems of the Disease model • Explains why behaviors are not normal within addicts – they are suffering from disease • Also explains why only some people become addicts – diseases only strike some individuals • No “diseases” have ever been identified, what kind they are, and how these diseases can make people take drugs
The Physical Dependence Model • Uses the phenomenon of withdrawal to explain why people are addicted to drugs • Sickness caused after drug cessation originally explained by autotoxin, a metabolite of the drug taken – really caused by physical dependence • Withdrawal sickness is exceptionally unpleasant, fear of withdrawal can explain the lengths drug abusers take to avoid going through it • Theory works well for abuse of opiates, alcohol, and barbiturates • Does not explain the use of many other drugs such as cocaine and cannabis which do not produce withdrawal sickness
Psychological Dependence • Physical dependence doesn’t explain all drug abuse; scientists theorized that something more subtle was occurring • Thought to take place in the brain and did not have any other symptoms other than it manifested itself as a craving • Circular argument – can’t say that psychological dependence causes drug abuse if you say that drug abuse causes psychological dependence • Need more proof, none exists for either physical or psychological dependence
Positive Reinforcement History • Until the 1950’s drug abuse was thought as a human disease, animals did not have free will and could not sin by using drugs (addiction was thought of as punishment) • Not reproducible because researchers used oral introduction when testing drugs • Delay between ingestion and effect of drugs which most likely affected learning • Most drugs have a bitter taste that animals dislike and most animals have built-in protection called flavor toxicosis learning which causes taste aversion if ingestion is followed by sickness or altercation in the nervous system
Positive Reinforcement History • During 1950’s researchers realized that laboratory animals learned to perform behavior that resulted in a drug injection • Drug infusion acted like a traditional positive reinforcer such as food or water (Thompson and Schuster 1964) • Positive reinforcer – any stimulus that increases the frequency of a behavior it is contingent on • Some drugs cause avoidance response due to their aversive properties – LSD, the antipsychotic drug chlorpromazine, and the antidepressant imipramine
Positive Reinforcement Problems • Positive Reinforcement Problems • Why can drug abuse be positive enough for some individuals to take the drug, while for others it will be adversive? • Why don’t punishing consequences have negative effects which counter the ones caused by drug abuse?
Positive Reinforcement • More traditional reinforcers such as food can be destructive and cause pain • People overeat and become obese which causes physical discomfort, health risks, and social censure • Sexual activity, gambling • Alcohol’s pleasure takes place soon after ingestion; hangovers occur hours later, learning has already occurred before someone gets sick
Reinforcement Centers • Reinforcement centers discovered in the brain associated with the limbic system that control the motivational behaviors of eating, drinking, and sexual activity
Reinforcement Center • Stimuli can act as reinforcers without the sensation of pleasure • Pleasure is caused by the activation of the mesolimbic dopamine system • The system exists not to make someone feel good, but to make them repeat certain actions
Reinforcing Effects of Drugs • Drugs can control behavior by utilizing the same brain mechanism as other reinforcers like food • Natural reinforcers have a satiation mechanism that terminates their reinforcing effect • Example: Food is only a reinforcer if there is hunger; after a certain amount is eaten food loses its value • Most drugs don’t appear to have any natural limits to their reinforcement
Drug use Between Human and Nonhuman Animals • Not a great deal of difference between species (Griffiths, Bigelow, and Henningfield 1980) • Nonhumans don’t find hallucinogens to be reinforcing, and do not readily self-administer the active ingredient in cannabis, THC
Incentive • Ability of drugs to act as reinforcers is not constant • Very tasty or nourishing foods can be powerful reinforcers while foods that are not so tasty or nourishing may only be of limited effectiveness • Foods may also only be reinforcers if an animal has been deprived of it for awhile
Incentive Value of Different Drugs • Drugs, like foods have different capacity to act as reinforcers – this property called abuse potential or abuse liability • Some drugs have varying durations of action • Other drugs such as Phenobarbital cause animals to go to sleep and cannot dose themselves again
Progressive Ratio, Choice, and Dose • Incentive problems can be overcome by using a progressive ratio schedule • Animals given a drug only after a certain behavior is exhibited (example: pulling a leaver) • Eventually can increase the quantity of behavior needed before reward given • Still has problems with drugs that can affect the behavior
Progressive Ratio, Choice, and Dose • Give animals two levers, keyed for a drug each • Given choice, animal should respond to lever that delivers more reinforcing drug • Larger doses generally more reinforcing than smaller doses, but when reach too large can be adversive
Genetic Differences • Positive reinforcement model emphasizes environmental and schedule variations are important to drug-self administration, but doesn’t preclude biochemical and genetic factors • Certain strains of mice have been bred to be alcohol-preferring or avoiding • Men with a family history of alcoholism are at greater risk of becoming alcoholics themselves (Schuckit 1985) • Different strains of rats and have been found to have preferences for cocaine and opiates
Relief of Unpleasant Symptoms • Use medications to relieve symptoms of stress • De Wit and Johnson (1987) diazepam (Valium) and placebo for normal population and then high anxiety population – no self-administration • Pirec et al 1995 – opiates will be self-administered if participants know they will experience pain
Task Demands • Use of drug depends on demands of expected situation • Silverman 1995 – color-coded capsules of a tranquilizer or stimulant • Participants either required to perform vigilance task or relaxation task • Seven of eight chose amphetamine with vigilance task, all eight with relaxation task
Stress • Stress like hunger can increase incentive value • Stress in animals can be caused by tail pinch, social isolation, exposure to aggression, and unpredictable foot shock • Stress hormones cause the release of dopamine in the nucleus accumbens and can act as reinforcers • Dopamine system stimulation intensifies incentive value of drug and related stimuli
Stress (continued) • Studies of US service personel in Vietnam showed many were using high-grade heroin on a regular basis, when returned to the US, many stopped
Previous Experience with Other Drugs – Gateway Drugs • Bergman and Johanson (1985) baboons do not self-administer diazepam when switched to it from cocaine • THC • Did when switched from pentobarbital
Physical dependence • Not necessary for drug-taking self administration, but withdrawal can influence the strength of the reinforcement • Tomoji Yangita (1987) compared breaking points between animals pretreated with a drug or placebo
Priming • Response to a reinforcer can be stimulated by noncontingent presentation of that reinforcer • J. Stewart and de Wit (1987) trained monkeys to press a bar for heroin or cocaine, stopped treatments • After one infusion, animals would start pressing the bar again • Priming explains loss of control in alcoholics • Exposure to a formerly abused drug causes both increased cravings and self-administration of the drug (relapse)
Place conditioning • Rats confined to one half of a box and given a drug – experience the drug in that location • When given opportunity to wander, spend more time in end of the box associated with reinforcing drugs – good indicator of reinforcing value of drug
Second-order schedules • First order (FR) is when reward is given after a certain number of responses • Second order is given in response to a FR • Example: Mouse presses a bar 20 times (FR20) to get a light to turn on – After light is lit 10 times (second order), they get reward of heroin injection – 200 injections total
Final Question • Using the positive reinforcement model, explain why nonhuman species avoid the hallucinogen LSD?