Substance Use disorders Flashcards
Substance use disorder (addiction): what happens to brain ?
Many brain areas affected
Substance use: why do we do it? ( D…)
Feels good! ( DOPAMINE)
Reward pathway: NA, VYA, mesolimbic sys.
Reward and +ve reinforcement (EER)
Initial exposure to certain drugs produce feelings of reward:
– Elation
– Excitement
- Relaxation
++ use > drug abuse > “Substance use disorder”
What is Substance Use Disorder? Solomons…
A compulsion to take drugs continuously or periodically
* Experience rewarding effects (A)
* Avoid the discomfort of its absence (B)
- see diagram slide 7: Solomon’s theory
Physical Vs Psychological dependence? ( W - H - C)
**DSM5: substance use disorder “one category” - continuum
1.Physical:
Stop taking the drug >withdrawal symptoms
* Heroin - abrupt cessation > sweating, goosepimples,
diarrhoea, muscular spasms, aches and pains
* Alcohol and benzodiazepines (valium) - hypersensitivity to sound/ light, anxiety, convulsions, coma …occasionally death (if withdrawal too abrupt)
- Psychological dependence
* Craving of the drug during abstinence
Components of Substance abuse disorders ? ( * Neuroadaptive processes / sensitisation)
Tolerance - loss of *effect of a drug (reward) with repeated administration
- Withdrawal - appearance of symptoms associated with termination of chronic drug use
- Neuroadaptive processes to counter the acute effects of the drug
(A key element in drug dependence is also sensitisation: * the increased ‘response’ to a drug following repeated
administration) - LONG TERM (chronic) : neuroadaptations :manifest after repeated drug administration
Liking vs wanting (Incentive-sensitization theory) + 4 main components)
Incentive-sensitization theory of addiction
- Compulsive drug use & inability to stop (relapse)
- ‘Excessive amplification’ of wanting the drug
- Less reliance on ‘liking’ the drug
4 Main components
* Addictive drugs : cause enduring neural adaptations
* Neural adaptations occur in regions involved in incentive motivation and reward (mesolimbic/mesocortical)
* These regions become hypersensitive (sensitized)
* But instead of sensitizing the reward (liking) component, drug ‘WANTING is now dominant. (The brain has changed to accommodate
maladaptive behaviour).
Dopamine( NA) & Addiction
* What makes a substance addictive? ( P + R)
Speed + magnitude of increased dopamine in the nucleus accumbens
…“RUSH”
Determined by:
* Potency
* Route of administration:
– Oral
– Subcutaneous
– Intramuscular
– Intranasal (snorting) – Inhalation
– Intravenous
Dopamine = REWARD
Theory of addiction ( Like vs Craving )
Lead to the hypothesis : if dopamine is causative of sensation of reward then it is responsible for addiction to abused substances
“Dopamine Theory of Addiction”…
Dopamine may make you LIKE to take drugs but is it responsible for obsessive CRAVING (NEED)?
What are 4 limitations of Dopamine theory of addiction? (
( A - DAT -Indiv. diff. - Craving)
- . Aversive stimuli such as the stress of handling, electric footshock, tailpinch or aggressive attacks increase dopamine transmission
- Mice lacking the dopamine transporter (DAT) will still self-administer cocaine (remember cocaine blocks the DAT)
DAT knockout (-/-) is determined by analysing the DNA sequence of a small piece of the mouse tail
(Hair colour gene can also be altered to help recognise gene depleted mouse)
!!Beware of data: developmental neural compensation may occur!!
- Individual differences - all abused drugs increase dopamine transmission but only a small percentage of people become addicted
A similar percentage of rats become ‘addicted’: individual differences between them exist (high responders vs low responders) - A major component of addiction is craving. Animal models of drug addiction (behavioural sensitisation and drug self- administration) show that the major neurotransmitter involved in craving is glutamate (learned associations with environmental cues - prefrontal & orbitofrontal cortex).
What are 2 symptoms of addiction? ( A -P)
Anxiety
* Depression
* Psychosis
Ø may be treated with available pharmacotherapies
Animal model of addiction ? ( Self-administration technique)
Common animal model of drug addiction is the drug ‘self- administration’ technique
Ø Animals (mice, rats, monkeys) will lever press to receive IV infusions of most drugs abused by humans (esp. cocaine, amphetamine, heroin, nicotine, but not LSD, THC?)
Ø Rats will self-administer alcohol orally
Ø Rats will also ‘self-stimulate’ brain areas associated with reward
Rats will self-administer cocaine until death (90%) - Heroin less toxic at 36% deaths (
*Rewarding effect of cocaine is blocked by:
Dopamine receptor antagonists
What Drives Addiction Processes?
There are very few effective pharmacotherapies for drug addiction
-particularly psychostimulants (cocaine, methamphetamine (“ice”)
Cocaine & Amphetamine - Repeated Use:( structure of brain and which function? Hippo, Dorsal Striatum, PFC, Orbitofrontal cortex)
Nucleus Accumbens: Motivation, Reward & Reinforcement
- Hippocampus & Amygdala: Memory & Emotion
- Dorsal Striatum: Decisions & Habit formation
- Prefrontal Cortex: Decisions & Control (appropriate behaviour)
- Orbitofrontal Cortex: Drive (value of reward)
Drug use increases activity in Striatum: activity correlates with perceived “rush
Ventral Striatum is Nucleus Accumbens
Dorsal Striatum is Caudate & Putamen
“Rush” is Euphoria
INC DA = INC Saliency of drug
Inflates reward prediction error
Addicts: DA response to natural rewards is reduced or absent!
