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Schizophrenia: brain chemicals

Schizophrenia: brain chemicals. How might neurotransmitters be implicated in mental illness?. Today’s session. Neurones. Neuronal cell bodies. Axons. Source: science photo library. Synapses occur at the junctions. Synapses. Neurones transmit signals electrically along their axons

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Schizophrenia: brain chemicals

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  1. Schizophrenia: brain chemicals • How might neurotransmitters be implicated in mental illness?

  2. Today’s session

  3. Neurones Neuronal cell bodies Axons Source: science photo library Synapses occur at the junctions

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

  5. Synapse Vesicles filled with neurotransmitter Synaptic cleft Source: neuroscience.wustl.edu Location of receptors (post-synaptic density)

  6. Vesicles release neurotransmitter into synaptic cleft

  7. Neurotransmitter binds to receptors & activates them

  8. Enzymes are released to break down the neurotransmitter

  9. Excess neurotransmitter is taken up by the pre-synaptic neurone

  10. Vesicles are replenished with new & reused neurotransmitter

  11. 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

  12. 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

  13. What could be done to make dopamine synapses less active?

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

  15. 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

  16. Side effects • Extrapyramidal side effects (EPS) • Parkinson’s-type symptoms • Postural & motor abnormalities • Other side effects • Sedation • Weight gain • Seizures

  17. What implications arise from the side effects of antipsychotic drugs?

  18. 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)

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

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