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Slide 29 -
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ADDICTION Lecture 12
CAPE
Password is
“dewleen”
Thursday Extra Credit-
See me after
class What is Drug Addiction? Not the same thing as drug abuse…
Hard to define, & definition has changed over the years. Modern definition of Addiction (Jaffe): “a behavioral pattern of drug use, characterized by
1) overwhelming involvement with the use of a drug (compulsive use) • does not necessarily imply that addiction = physical dependence (many addictive drugs do not produce much physical dependence) the securing of its supply (compulsive drug-seeking), & 3) a high tendency to relapse after withdrawal” Addiction Outline Theories of addiction
a) Negative Reinforcement Models
Physical dependence (withdrawal) theory
–driven largely by opiates, barbiturates, alcohol
–based largely on tolerance and physical dependence
Self-Medication Hypothesis b) Positive Reinforcement Models
Positive incentive (reward) theory
–driven largely by cocaine, amphetamine, nicotine
–based largely on reward and reinforcement 2. Common mechanism of addiction/reward
--pathways in the brain Opiates & addiction: Because it hurts to quit? Why are some opiates addictive?
Original explanation: Physical Dependence Theory of Addiction:
Stop taking opiates -> physical withdrawal -> start drug again Withdrawal: marked physiological disturbance that occurs upon cessation of the drug; OPPOSITE of drug effects •Withdrawal syndrome is due to physical dependence Physical dependence: withdrawal occurs upon cessation of the drug Physical dependence occurs because of homeostasis
•Body tries to compensate for changes caused by taking
the drug Physical dependence & withdrawal syndrome Example:
1. temperature goes up when take drug
2. body has a set point (homeostasis) for temperature & compensatory changes bring it back to set point Opiates and past theories of addiction •Bodily compensatory changes develop over time, with
drug use These compensations form the basis for tolerance:
drug effect gets weaker with repeated administration, OR the need to take more drug to get the same effect. So at a certain time in history (1970s), dependence and tolerance were the basis for addiction… Physical dependence theory Take drugs to avoid unpleasant consequences of withdrawal:
Physical dependence theory of addiction Take drug -> nasty withdrawal goes away
So by this theory, if you treat withdrawal (or wait for it to go away), you treat addiction. •Note that this theory assumes addiction = dependence •Escalating drug use is attributed to tolerance Alcohol also fits the physical dependence model of addiction… •Alcohol activates GABA-A receptor (among other actions); causes IPSP (inhibitory) •Produces severe dependence & very severe withdrawal
(Life Threatening: seizures & delirium tremens or DTs)
•much > severe than opiates
Works well for Opiates, Barbiturates, & Alcohol, not stimulants
Problems with the Physical dependence theory 1. No good relationship between strength of withdrawal & strength of addiction: Withdrawal: alcohol and barb worse than heroin
Addiction: heroin more addictive than alcohol or barb
Changing the rise time of the drug (e.g., route of admin)
has no effect on physical dependence but big efffect
on addiction Can treat withdrawal (wait for it to go away - detox), but
addiction remains. Relapse very high even years later. Drugs that do not produce much dependence (withdrawal) still very addictive: Amphetamine, Cocaine, Nicotine
- probably more so than the other drugs
- do not confuse craving with withdrawal
4. Only very high doses of drugs produce dependence An alternative model of addiction Positive incentive theory of addiction:
Positive reinforcement - response that is followed by pleasant consequences likely to be repeated • Take drug to get euphoria or drug "high" • Can account for addictiveness (most to least): Amphetamine > Heroin = Cocaine > Nicotine > Alcohol • Also can account for difference in heroin & morphine… Positive incentive theory & the delay of reinforcement gradient Heroin is converted to morphine in the brain.
•Main difference = speed with which drug gets into brain
(heroin faster than morphine). This is critical to abuse potential: • E.g., injection > inhale > pill
e.g., crack cocaine vs snorting
• many non-addictive versions of drugs are simply ones where
drug onset is slow
(e.g., crystal meth vs. desoxyn(time release)) • Key concept in ALL reinforcement =
Delay of Reinforcement Gradient: inverse relationship between delay & reinforcing properties
(GREATER delay of onset = LESS reinforcing) I.V. cocaine is most addictive, oral is least IV oral time blood plasma cocaine concentration Measuring the reinforcing properties of drugs Problem was no good way to measure reinforcement in animals (easy to measure withdrawal)… In the late 60's two models developed:
Self-administration paradigm
2. Conditioned place preference Self-Administration Model (“drug taking”)
The rat presses the lever to self-inject a drug, either
Into an area of its brain or into general circulation Conditioned Place Preference Model (“drug seeking”)
A rat repeatedly receives a drug in 1 of 2 distinctive
compartments. Then, on the test, the tendency of the rat,
now drug-free, to prefer the drug compartment is assessed. Positive incentive theory & animal studies • Animal work in these 2 positive reinforcement models
lined up well with addict reports. Liked:
amphetamine > cocaine = heroin >
nicotine > alcohol • could also discriminate b/w morphine & heroin
(heroin > addictive) Interest shifted to amphetamine and cocaine… Mechanisms of action of cocaine and amph Amphetamine & cocaine’s actions on dopamine
(DA) are the key to their reinforcing qualities. Cocaine jams the DA reuptake pump (“DA
transporter”), released DA stays active longer Amphetamine reverses the DA transporter, dumping
large pools of cytoplasmic DA into the synapse Nicotine and dopamine’s role in addiction Nicotine acts on acetylcoline (Ach) receptors…but this also leads to enhanced DA release. **ALL reinforcers (food, sex, etc.) seem to activate
DA release Dopamine’s role in addiction: addictive drugs
"hijack" the natural reinforcement pathway What is this pathway? The Dopamine VTA-Accumbens and Accumbens-Prefrontal Cortex Pathways are KEY Planning
Inhibition
Self-control Reward Emotional memory Prefrontal
cortex Ventral
tegmental
area nucleus
accumbens amygdala Cocaine & Amphetamine directly activate DA in the accumbens Time (hours)
Cocaine Self-injections Time (hours)
Amphetamine Self-injections Dopamine concentration in the nucleus accumbens of rats Drugs that increase
extracellular dopamine
amphetamine
cocaine
opiates (morphine, heroin)
MDMA
ethanol (alcohol)
PCP
nicotine ethanol nicotine morphine amphetamine cocaine accumbens accumbens Drugs abused by humans preferentially increase synaptic dopamine
concentrations in the mesolimbic system of freely moving rats Sensitization But what supports pattern of escalating use? (from Anagnostaras, Schallert, & Robinson, 2001) Behavioral sensitization Amphetamine injections
in rats sensitize psychomotor
(rotation/activity) response Some drug EFFECTS show sensitization, the opposite of tolerance (“reverse tolerance”) •True of DA release & DA effects of drugs. From the previous graph:
• The longer a rat is treated with amphetamine
(i.e., 3 days vs. 28 days), the more DA that is
released when a “test” amphetamine injection is given
at a later time…. So, cellular DA release sensitizes • This could be the cellular basis for what addicts
define as “craving” • The memory of how good the high was sensitizes in
addicts… Sensitization & increased drug use • Incentive-Sensitization Theory:
escalating drug use is due to sensitization of positive-
incentive value of the drug
(ie., increased “craving” or “wanting”) • No known way to reverse sensitization • Lasts long after withdrawal (seems to last forever) • Major focus is to develop treatments to block and
reverse neural (cellular) sensitization in brain Problems with Positive Incentive Theory 1. Doesn't address relapse, at least in this form:
Why do addicts start taking the drug again long after they quit? maybe reminder cues/drug context?? we know that drug-related cues (alone) can cause
DA release in the brain…. Classical conditioning in Pavlov’s dogs 1. Before conditioning 2, Before conditioning 3. During conditioning 4. After conditioning Food response response response response salivation salivation No salivation salivation Tuning fork Tuning fork Unconditioned
stimulus Unconditioned
response Unconditioned
response Conditioned
response Conditioned
stimulus No conditioned
response Neutral
stimulus Tuning fork Food Conditioning of drug-like effects: contributing to relapse? Sight of syringe, needle, room, etc. Initial exposure Neutral stimuli Drug (e.g.,
Amphetamine) US UR Later effects CS DA release, activity, etc. Sight of stimuli
associated w/drug taking DA release, activity CR Anagnostaras & Robinson, 1996 Relapse-Positive Reinforcement View CS produces “drug-like” effect
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