Chapter 5: Drugs, Addiction, and Reward
Chapter Summary, Outline, and Key Terms
Psychoactive
Drugs
A
drug is a substance that on entering the body
changes the body or its functioning
An
agonist mimics or enhances the effect of a
neurotransmitter
An
antagonist reduces the effects of a
neurotransmitter
Psychoactive drugs have psychological effects
Addiction is defined as a preoccupation with
obtaining a drug, compulsive use of the drug,
and
a high tendency to relapse after quitting
Withdrawal is a negative reaction that occurs
when drug use is stopped, typically the opposite
of the drug’s effects
Tolerance occurs when increasing amounts of a
drug are needed to produce the same effects as
before
Most is due
to a reduction in receptors, or
reduction in sensitivity of the receptors
Tolerance
may occur to some effects of a drug
and not others
Opiates
are drugs derived from opium, which comes
from the poppy flower
Effects : Analgesic (pain relieving)
Hypnotic (sleep-inducing)
Euphoria-inducing
Types:
Opium, Morphine, Heroin and Codeine
Effects
of heroin
Crosses the
blood-brain barrier easily
Creates
euphoria, followed by relaxation and
contentment
Fosters long-term addiction
Novelty (new
environment) can increase effects
Binds to
endorphin receptors in the brain
Depressants
are drugs that reduce central nervous system activity
Effects:
Sedative (calming)
Anxiolytic (anxiety-reducing)
Hypnotic
Alcohol
Alcohol acts
at several brain sites
Produces
euphoria, anxiety reduction, loss of motor coordination, and cognitive impairment
In small doses,
acts as a stimulant. In larger
doses becomes a sedative
Alcohol use
is commonly associated with
violent crime, in part because it reduces the
anxiety that normally stops aggression from
occurring
Alcoholism
is commonly associated with
cirrhosis of the liver
Korsakoff’s syndrome from vitamin B1
deficiency
Withdrawing
from alcohol can involve several
disturbances, including delirium tremens
(hallucinations, delusions, etc.)
Alcohol inhibits
the glutamate release and
increases GABA release
Alcohol targets
a receptor of the GABAA
complex
Fetal Alcohol
Syndrome (FAS)
Alcohol
passes easily into a fetus from a
mother’s bloodstream
No
safe level has been established for
alcohol intake during pregnancy
FAS is the
leading cause of mental
retardation in the western world
Barbiturates
and Benzodiazepines reduce
anxiety, but not pain
Barbiturates act on higher cortical centers that
inhibit behavior
Barbiturates Increase talkativeness and social
interaction
Reduce anxiety
and act as hypnotics in high doses
Inhibit
glutamate activity
Enhance activity
at the GABAA receptor complex,
like alcohol, but via a different receptor
Addictive, and fatal in large doses
Benzodiazepines have similar effects to
barbiturates but are safer.
Act through GABAA
receptors to suppress activity in the limbic system
without increasing chloride influx
Produce sedative, muscle-relaxing effects and are
also addictive
Stimulants
Produce
arousal, increased alertness, and elevated
mood
Include a
wide range of drugs which are different in
terms of risk
Cocaine is extracted from the coca plant
Produces euphoria,
decreased appetite,
increased alertness and relief from fatigue.
Blocks the
reuptake of dopamine and serotonin
potentiating their effects.
Withdrawal
effects are relatively mild and
include depression, anxiety and boredom,
which motivates further use
Cocaine
is one of the most addictive drugs,
and no treatment is considered successful
Regular
use can produce brain damage,
seizure and death
It passes
through the placenta and affects IQ,
language development, and distractibility in
exposed children
Amphetamines are synthetic drugs that
produce euphoria and increased
confidence/concentration.
Include Benzedrine, Dexedrine, and
methamphetamine
Reduce appetite
and fatigue, and increase
alertness
Increase the
release of norepinephrine and
dopamine
With chronic
use, can cause hallucinations and
delusions similar to paranoid schizophrenia
Nicotine
The primary psychoactive agent in tobacco
In large doses
causes nausea, vomiting and
headaches
Withdrawal
symptoms include nervousness,
anxiety, drowsiness, lightheadedness and
headaches
A highly addictive
drug
Smoking
Non-nicotine ingredients cause breathing
difficulty, coughing, bronchial tract infections,
pneumonia, bronchitis, emphysema, and cancer
Children of
mothers who smoke have twice the
rate of conduct disorder, and a higher than
normal rate of criminal activity
Nicotine stimulates nicotinic acetylcholine
receptors
Caffeine produces arousal
and increased
alertness
Blocks adenosine receptors
Increases dopamine and acetylcholine release
Withdrawal symptoms include headaches,
fatigue, anxiety, shakiness and craving
Psychedelic
drugs cause perceptual distortions (also
known as hallucinogenics)
Lisergic
acid diethylaminde (LSD) is structurally
similar to serotonin and stimulates serotonin receptors
Psilocybin
and psilocin (from the mushroom Psilocybe
mexicana) are only 1/200 as strong as LSD
Mescaline
(peyote) resembles norepinephrine but also
activates serotonin receptors
Methylenedioxymethamphetamine
(MDMA, or
Ecstasy) increases serotonin and dopamine release
Phencyclidine
(PCP, or angel dust) inhibits glutamate
receptors, and blocks reuptake of dopamine
Marijuana is from the Indian hemp plant Cannabis
sativa
Primary psychoactive component:
delta-9- tetrahydrocannabinol (THC)
THC binds to cannabinoid receptors throughout the
CNS
THC increases dopamine levels
Prenatal exposure can result in
behavioral problems
later in life
Argued to produce only psychological dependence,
but evidence for physical addiction exists
Addiction
The Neural
Basis of Addiction
Addiction
and withdrawal are independent
phenomena
Addiction to drugs depends on reward (positive reward effects)
The mesolimbic
dopamine system contains the
primary drug reward structures (nucleus
accumbens, medial forebrain bundle,
ventral
tegmental area)
Dopamine and
Reward
Most abused drugs increase dopamine levels in the
nucleus accumbens
Electrical stimulation of the brain (ESB), has been
used to identify regions
of endogenous reward.
Addicts have fewer D2 receptors and reduced
dopamine release, creating a “reward deficiency
syndrome” that may precede abuse and predispose
these individuals to addiction
Dopamine does not account for all reward, and is
not the only neurotransmitter responsible for
addiction
C. Roles for Dopamine
Dopamine’s
effect may involve more than reward
Dopamine neurons
respond to the unpredictability
of rewards
Dopamine neurons
report errors in prediction
Dopamine plays
a role in learning, including
drug-related learning
Dopamine release
in the prefrontal cortex can
generate cravings for drugs.
Treating Drug Addiction
First - Detoxification
Treatment for Addiction Strategies
Agonist treatments
replace an addicting drug with
another drug with similar effects, such as methadone
for opiate addiction
Antagonist
treatments involve drugs that block the
effects of the addicting drug
Naltrexone
is used to control opiate addiction
Aaddict must be motivated to quit, because antagonists
do not replace the effect of the original drug
Aversive
treatments cause a negative reaction
when the person takes the addicting drug
Antabuse combats alcohol addiction
Anti-drug vaccines, synthetic molecules that resemble
the original drug, modify the immune system to create anti-drug antibodies
Decreased
serotonin levels are associated with several addictions
Neurotransmitter systems are highly interconnected, thus a wide variety of drugs are available to treat addiction
Pharmacological Treatment: Treating heroin addiction with a combination of methadone and counseling is far more successful than counseling alone
Addiction is often linked to personality disorders, thus treating the underlying disorder may also help
relieve the addiction
Use of pharmacological
drugs to treat addiction is controversial when it involves replacing the drug with a similar drug or does not require exercise
of will
The Role of Genes in Addiction
Separating Genetic and Environmental Influences
Late onset (Type 1) alcoholics begin their addiction after the age of 25
Can abstain most of the time
Binge drinkers
Feel
guilty
Early onset
(Type 2) alcoholics begin drinking at
an early age
Drink often
Do not
feel guilty
Have a tendency
toward antisocial behavior
Are almost
entirely male
Environmental interactions are often variable
Heritability
for alcoholism is around 50-60%
Genes
can affect risk for addiction to specific
drugs or a spectrum
Alleles
are alternate forms of a gene
Alcoholics
commonly have the A1 allele of the D2
receptor gene, resulting in fewer D2 receptors
Various alleles
of the D2 form of the dopamine
receptor gene have been associated with a
variety of addictions
Individuals
with a deficiency in aldehyde
dehydrogenase are less able to metabolize
alcohol and thus less likely to become addicted
Serotonin
affects mood, sexual behavior,
aggression, and the regulation of bodily rhythms
Serotonin functioning is lower in alcoholics
Alcohol
stimulates serotonin pathways, thus
temporarily improving mood
Serotonin
activates dopamine pathways,
probably enhancing reward
Drugs that
block serotonin receptors reduce
some of the effects of alcohol, and craving and
consumption
Implications
of Alcoholism Research
Studying
alcoholism shows general principles of
behavioral inheritance
Studying
alcoholism is a good preparation for
inquiries into the other physiological systems
