Lecture 6: Psychiatric Disorders, Drug Action and Addiction Flashcards
What are drugs?
- Substances similar to substances already present in our nervous systems.
- Particularly similar to those affecting at the synapse.
- Substances present in the natural world - mainly from plants.
- Plants produce the chemicals to attract/repel insects or for own process.
- Nervous systems of animals are very similar so also act on humans.
How do drugs work?
- Facilitate or inhibit transmission of nerve impulse at the synapse.
- Drug has high affinity for a receptor if it binds to it (may not activate the receptor)
- Drug has high efficacy if activates the receptor.
- Most drugs stimulate the release of dopamine.
- Particularly in the nucleus accumbens (reward centre).
- Area rich in dopamine receptors.
- Drug -> sustained bursts of dopamine (usually inhibitory) -> inhibits GABA (gamma - aminobutyric acid, important inhibitory transmitter) -> increases in nucleus accumbens.
What are the effects of Agonistic drugs?
- Increases synthesis of NT.
- Increases the number of the NT by destroying degrading enzymes.
- Increases the release of NT.
- Binds to presynaptic receptors and block inhibitory effect.
- Binds to postsynaptic receptors and activates or increases the NT effect.
- Blocks the deactivation of NT by blocking their degradation or reuptake.
What are the effects of Antagonistic drugs?
- Block synthesis of NT.
- Causes the NT to leak and to be destroyed.
- Blocks the release of NT.
- Activates the receptors and inhibits NT release.
- Binds to receptors and blocks the effects of NT.
How do stimulant drugs work?
*Amphetamine (speed): Stimulates dopamine synapses by increasing the release of dopamine from presynaptic terminal.
*Cocaine: Blocks the reuptake of dopamine, thus prolonging effects.
= Dopamine agonists.
*Accumulation of dopamine in the synaptic cleft.
*More dopamine = widespread reduction in activity in most of the brain (except nucleus accumbens).
How do Opiates drugs work?
- Increases relaxation, decrease sensitivity to pain.
- Morphine
- Heroine
- Codeine
- Mimic endorphins (naturally occurring chemicals in the brain).
- Attach to endorphins receptors
- increase dopamine
- Also blocks hindbrain area that normally release norepinephrine.
- Reduces memory storage and stress.
How does Marijuana work?
- Contains cannabinoids
- Binds to specific receptors.
- Inhibits GABA release
- Increase in dopamine release
- perception of heightened awareness.
- Receptors are abundant in hypothalamus (feeding).
- increases appetite.
How does Botox (Botulinum toxin) work?
- Deadly neurotoxin released by bacteria found in decaying food.
- Antagonist
- Blocks the release of acetylcholine at neuromuscular junctions - paralysis.
- But, in small doses can be used to reduce muscle tremors and cosmetically.
What is addiction?
- Many addictive substances increase activity at dopamine synapses.
- Particularly in the nucleus accumbens.
- Drugs increase need for the substance even if the experience is not pleasant.
- Addiction can be hard to define, particularly when it relates to legal, socially acceptable substances.
- Addiction = continued use of a substance when it interferes with your life.
- Alcohol acts on many areas of the brain - mainly inhibitory effects.
What is drug tolerance?
- Pleasurable effects decrease as addiction develops.
- can lead to increase in drug intake.
- Learned.
What is drug withdrawal?
- Cravings for the drug
- Relapse causes increased sensitivity
- User learns that the drug relieves distress associated with withdrawal, and so craves it more during future withdrawal.
What are the two types of alcoholism?
- Type 1:
- Late onset (afer 25)
- Gradual onset
- Equal men and women
- Less severe
- Type 2:
- Early onset (before 25)
- Rapid onset
- More men than women
- severe.
How might Genes influence alcoholism?
- Coding for an increase in risk taking behaviour.
2. Coding for an increased stress response = more likely to relapse after quitting.
Do sons of alcoholic fathers show predispositions to to alcoholism?
- Show less than average intoxication - tolerance to alcohol.
- Show greater decrease of stress when drinking.
- Slightly smaller amygdala (therefore increased risk taking).
What is depression?
- Feelings of extreme sadness and helplessness.
- Severe enough to interfere with daily life, and can last for weeks or months rather than days.
- The absence of happiness.
- Twice as common in women than men.
- 5% adults have clinically significant depression.
What causes depression?
- Life experiences or biological propensity?
- Moderate degree of heritability to depression (fu et al., 2002).
- But not specific to depression - relatives also more likely to suffer from anxiety disorders, substance abuse, bulimia.
- More common among relatives of women with early onset depression (before 30).
What effect does Serotonin have on depression?
- Low serotonin turnover associated with aggression and depression.
- so genes controlling serotonin have been implicated.
- Gene controlling the serotonin transporter protein.
- This protein controls ability of an axon to reabsorb serotonin.
- Short and long types.
- If you have two short forms of the gene = more likely to have depression in response to stressful events.
What is Bipolar disorder?
- Unipolar disorder: varying between normality and depression.
- Bipolar disorder: varying between mania and depression (Mania = restless activity, excitement, confidence, rambling speech).
- Increased metabolism during manic phases (PET scans)
- Possible genetic component - more common in monozygotic twins, but this seems to increase risk rather than cause.
- Treated with lithium salts
- block synthesis of arachidonic acid (associated with brain inflammation).
What is Seasonal Affective disorder?
- Depression associated with one season (usually winter).
- Common near the poles where the nights are long.
- Less severe than major depression
- Light therapy as treatment (affects biological clock).
What is schizophrenia?
- Split mind - but is NOT related to multiple personality disorder.
- The split refers to a division between emotional and intellectual experiences and behaviour.
- some patients show inappropriate emotional expression that seems detached from current circumstances.
- Other symptoms: hallucinations, delusions, thought disorders, movement disorders.
- can be acute or chronic.
- Not all patients exhibits all symptoms.
- Difficult to diagnose, often confused with other conditions.
- but, PET scans have found activation in in thalamus, hippocampus and auditory cortex during hallucinations
- Impairments on tasks remembering rules implies problems with the hippocampus.
- More common in men.
- Earlier onset in men.
- Present in 1% of the population (2011).
- Equal proportions in all cultures/populations (although more diagnoses in developed countries).
- More likely in closely related individuals.
- More likely in closely related individuals.
How does schizophrenia develop?
- Neurodevelopmental hypothesis
- Abnormalities in the development of the nervous system before birth (prenatal) and in the newborn.
- Infections, poor nutrition, complicated delivery, BUT, only increases chance of schizophrenia slightly.
- Some slight brain abnormalities in patients, suggesting subtle changes during development.
How is schizophrenia associated brain anomalies?
- Ventricles (fluid - filled spaces in the brain) larger, so less space for brain cells.
- Prefrontal cortex damaged (working memory impaired).
- Cell bodies are smaller in the hippocampus and prefrontal cortex (memory consolidation and working memory).
- Less lateralisation than most people
- implication for language deficit
- More likely to be left handed.
How is schizophrenia at the level of the synapse?
- Abuse drugs are associated with an excess of dopamine, and can cause psychosis.
- Dopamine hypothesis of schizophrenia = excess activity of dopamine synapses.
- Schizophrenia patients have twice as many dopamine receptors than other people.
- But, normal levels of dopamine are found when measured directly.
- Schizophrenia is also associated with lower than normal release of glutamate and fewer receptors in the prefrontal cortex.
- Glutamate hypothesis of schizophrenia = deficient activity at glutamate and fewer receptors in the prefrontal cortex.
- related to dopamine - dopamine inhibits glutamate release and glutamate activates neurons than inhibits dopamine.
- Phencyclidine (PCP, angel dust) inhibits glutamate receptors and procedures similar to symptoms to schizophrenia (hallucinations, thought disorder, memory loss.