LECTURE 5 DRUGS AND ALTERED CONSCIOUSNESS

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LECTURE 5DRUGS AND ALTERED CONSCIOUSNESS

• (this material is covered in Drugs and
  Behaviour section of chapter 4, Martin et al)
• David Pearson
• Room T10, William Guild Building
• Email d.g.pearson_at_abdn.ac.uk

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• The brain is protected by a tightly packed lining
  of cells called the blood-brain barrier.
• However, some drugs are able to pass through and
  influence the operation of the brain.
• These drugs alter consciousness by facilitating
  or inhibiting synaptic transmission.

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Basic Steps in Synaptic Transmission

• Neurotransmitters are synthesized in the
  presynaptic (sending) neuron and stored in
  vesicles.
• Neurotransmitters are released into the synapse,
  where they stimulate receptor sites on the
  postsynaptic (receiving) neuron.
• Neurotransmitters are deactivated by enzymes or
  by reuptake.

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• Drugs that affect synaptic transmission can be
  divided into two main categories
• Agonist drugs
• Antagonist drugs

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Agonist Drugs

• Agonist drugs work by increasing the activity of
  a neurotransmitter.
• This can be done by
• Enhancing a neurons ability to synthesize,
  store, or release neurotransmitters.
• Binding with and stimulating postsynaptic
  receptor sites (or increasing sensitivity of
  these sites)
• Prolonging activity of neurotransmitters (e.g.,
  by inhibiting reuptake)

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Example of Agonist Action

• The brain produces natural pain-killing chemicals
  called endorphins.
• Drugs known as opiates (e.g., morphine, codeine)
  have a molecular structure similar to that of
  endorphins.
• Opiates can therefore bind to and activate
  receptor sites that normally receive endorphins,
  and duplicate their effects.

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Antagonist Drugs

• Antagonist drugs work by inhibiting or decreasing
  the action of neurotransmitters.
• This can be done by
• Reducing a neurons ability to synthesize, store,
  or release neurotransmitters
• Preventing a neurotransmitter from binding with
  the postsynaptic neuron (e.g., by blocking the
  receptor sites)

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Example of Antagonist Action

• Symptoms of schizophrenia (hallucinations,
  delusions etc.) are often associated with
  abnormal overactivity of the neurotransmitter
  dopamine.
• Antipsychotic drugs have a molecular structure
  similar enough to dopamine to block the receptor
  sites, but not similar enough to activate them.

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Consciousness-Altering Drugs

• Depressants
• Stimulants
• Hallucinogens

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Depressants

• Depressants work by decreasing nervous system
  activity.
• In moderate doses depressants reduce feelings of
  tension and anxiety, and produce a state of
  relaxed euphoria.
• In high doses depressants can slow down vital
  life processes to the point of death.

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Alcohol
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• Alcohol increases the activity of
  gamma-aminobutyric acid (GABA), a major
  inhibitory neurotransmitter.
• Alcohol also decreases the activity of glutamate,
  which is a major excitatory neurotransmitter.
• Together these effects produce a substantial
  reduction in neural firing within the brain.

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• Neural slowdown reduces activity in the
  inhibitory control centres in the cerebral
  cortex.
• This leads to disinhibition and feelings of
  euphoria.
• At higher dosage disruption of cerebral control
  centres produces disorganised thinking and
  physical coordination, fatigue, and psychological
  depression.

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• Alcohol also produces an effect known as alcohol
  myopia (Steel Josephs, 1990).
• Neural slowdown produces an increased inability
  to attend to and process new information.
• Drinkers begin to pay attention only to those
  aspects of a situation (cues) that stand out, and
  ignore other relevant information.
• This produces an increase in risk-taking
  behaviour and a failure to attend to long-term
  consequences of actions (MacDonald et al., 2000).

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Stimulants

• Amphetamines
• Amphetamines can reduce appetite and fatigue,
  decrease the need for sleep, and in some cases
  reduce feelings of depression.
• Amphetamines increase the activity of the
  neurotransmitters dopamine and norepinephrine.
• This is done by (a) causing the neuron to release
  greater amounts of these neurotransmitters, and
  (b) inhibiting reuptake.

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• Adverse effects of amphetamines include increased
  blood pressure, heart failure, cerebral
  hemorrhage.
• Repeated high doses can result in long-term brain
  damage (Diaz, 1997).
• Continuous heavy amphetamine use can result in
  amphetamine psychosis (Lynn, 1971).
• Heavy amphetamine use is linked to severe
  withdrawal symptoms (crash) due to depletion of
  dopamine and norepinephrine reserves.

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• Cocaine
• Cocaine is a natural stimulant derived from the
  coca plant (also synthetic version novocain).
• It produces excitation, sense of increased
  muscular strength, and euphoria.
• Works by blocking reuptake of dopamine and
  norepinephrine.
• In large doses produces fever, vomiting,
  convulsions, hallucinations, and paranoid
  delusions.

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• Historically cocaine was hailed as a wonder
  drug and widely used as a local anaesthetic and
  general stimulant.
• In 1885 John Pemberton developed a mixture of
  cocaine, syrup, and kola nut extract and marketed
  it as health tonic.

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• By 1891 there was a growing national debate in
  the USA about the negative aspects of cocaine.
• By 1902 Coca-cola contained only 1/400 of a grain
  of cocaine per ounce of syrup.
• Cocaine not completely removed until 1929.

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Hallucinogens

• In 1943 Swiss chemist Albert Hofmann accidentally
  absorbed a new chemical that he was synthesising
• The dizzinessbecame so strong at times that
  Ihad to lie down on a sofaEverything in the
  room spun around and the familiar objects and
  pieces of furniture assumed grotesque, mostly
  threatening forms.
• Hoffman had synthesised lysergic acid
  diethylamide (LSD).

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• We were somewhere around Barstow on the edge of
  the desert when the drugs began to take hold. I
  remember saying something like I feel a bit
  lightheaded maybe you should drive And
  suddenly there was a terrible roar all around us
  and the sky was full of what looked like huge
  bats, all swooping and screeching and diving
  around the car, which was going about a hundred
  miles an hour with the top down to Las Vegas.
• Hunter S. Thompson
• Fear and Loathing in Las Vegas

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• Hallucinogens are powerful consciousness-altering
  drugs that produce substantial hallucinations.
• Natural Hallucinogens
• Mescaline (peyote cactus extract)
• Psilocybin (magic mushrooms)
• Synthetic
• LSD
• Phencyclidine (Angel Dust)

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• Hallucinogenic effects include distorted or
  intensified sensory experience, synaesthesia,
  mystical experiences and insights,
  exhilaration.
• Adverse effects can include violent outbursts,
  paranoia, panic, and flashbacks long after the
  drugs effects have apparently ended.

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• Molecular structure of LSD is very similar to the
  neurotransmitter serotonin.
• Overall LSD decreases serotonin activity.
• During normal sleep decreased serotonin levels
  are linked to the onset of REM sleep.
• Some argue that LSDs inhibition of serotonin
  allows dreamlike altered perceptions and
  hallucinations to emerge while we are still awake
  (Trulson Jacobs, 1979).

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Summary

• Drugs can alter consciousness by facilitating or
  inhibiting synaptic transmission in the brain.
• Agonist drugs increase the activity of
  neurotransmitters.
• Antagonist drugs inhibit or decrease the activity
  of neurotransmitters.