Schizophrenia: brain chemicals

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Schizophrenia brain chemicals

• How might neurotransmitters be implicated in
  mental illness?

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Todays session
You will learn about Context
Commenting on evidence Synaptic transmission Drug treatments for psychological disorders Schizophrenia The dopamine hypothesis of schizophrenia
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Neurones
Neuronal cell bodies
Axons
Source science photo library
Synapses occur at the junctions
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Synapses

• Neurones transmit signals electrically along
  their axons
• The synapses (junctions between neurones)
  transmit signals chemically

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Synapse
Vesicles filled with neurotransmitter
Synaptic cleft
Source neuroscience.wustl.edu
Location of receptors (post-synaptic density)
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Vesicles release neurotransmitter into synaptic
cleft
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Neurotransmitter binds to receptors activates
them
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Enzymes are released to break down the
neurotransmitter
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Excess neurotransmitter is taken up by the
pre-synaptic neurone
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Vesicles are replenished with new reused
neurotransmitter
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The dopamine hypothesis

• Schizophrenia is caused by excessive activity at
  synapses that use dopamine as their primary
  neurotransmitter
• This causes abnormal functioning of DA-dependent
  brain systems, resulting in schizophrenic symptoms

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Biology and Schizophrenia

• Consistent evidence for abnormal brain
  functioning in S patients but no single factor
  identified.
• Two syndromes?
• Cause effect issues everywhere
• Confounding effects of drug treatment

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• What could be done to make dopamine synapses less
  active?

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Antipsychotic medication

• Neuroleptics (e.g. chlorpromazine) bind to DA
  receptors without activating them

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Effectiveness

• Older (typical) drugs (e.g. chlorpromazine)
• Short term beneficial effect in 75 of patients
  (Davis et al, 1989)
• Long term beneficial effect in 55-60 (Davis et
  al, 1993)
• Most effective against positive symptoms
• High risk of side effects

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Side effects

• Extrapyramidal side effects (EPS)
• Parkinsons-type symptoms
• Postural motor abnormalities
• Other side effects
• Sedation
• Weight gain
• Seizures

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• What implications arise from the side effects of
  antipsychotic drugs?

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Effectiveness

• Newer (atypical) drugs (e.g. clozapine)
• As effective as typical drugs on positive
  symptoms better for negative symptoms (Bilder et
  al, 2002)
• More effective with treatment-resistant patients
  (DeNayer et al, 2003)
• Less risk of EPS, but other side effects may
  occur (e.g. blood disorders)

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Typical vs. atypical
tightly bound slow release from receptor
loosely bound fast release from receptor
DA receptor
Drug