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.