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Synaptic transmission
Mechanisms of drug action
Drugs used with schizophrenia
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Schizophrenia: drugs
Neuronal cell
bodies
Axons
Synapses occur
at the junctions
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Source: science photo library
Neurones
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Neurones transmit signals electrically along
their axons
The synapses (junctions between neurones)
transmit signals chemically
Most drugs act by interfering with events at
the synapse
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Synapses
Source: neuroscience.wustl.edu
Vesicles filled with
neurotransmitter
Synaptic cleft
Location of
receptors (postsynaptic density)
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Synapse
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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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Increase synaptic activity by:
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Causing more neurotransmitter to be released
Introducing a chemical that acts like the
neurotransmitter
Preventing breakdown of neurotransmitter
Preventing reuptake of neurotransmitter
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Drug Therapies
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Decrease activity by:
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Increasing rate of neurotransmitter breakdown
Blocking off receptors
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Drug therapies
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Neuroleptics (e.g. chlorpromazine) bind to DA
receptors without activating them
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Antipsychotic medication
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Older (typical) drugs (e.g. chlorpromazine)
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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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Effectiveness
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Extrapyramidal side effects (EPS)
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Parkinson’s-type symptoms
Postural & motor abnormalities
Other side effects
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Sedation
Weight gain
Seizures
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Side effects
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Newer (atypical) drugs (e.g. clozapine)
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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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Effectiveness
tightly bound;
slow release from
receptor
DA receptor
Drug
loosely bound;
fast release from
receptor
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Typical vs. atypical