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Chapter 16
Schizophrenia
http://www.npr.org/programs/atc/features/2002/aug/schizophrenia/
18.2 Treatment of the mentally ill
• Schizophrenia
– A serious mental disorder characterized by disordered thoughts, delusions, hallucinations, and mood disturbance.
Schizophrenia
• Positive Symptoms– Delusions– Hallucinations– Disorganized behavior
• Negative Symptoms– Social withdrawal– Mood disturbance– Reduced motivation
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• Schizophrenia–Positive symptoms
–Dopamine hypothesis:• Overactivity of dopamine in
mesolimbic pathway (VTA to nucleus accumbens and amygdala)
• Schizophrenia– How are positive symptoms related to
dopamine?
– Hypothesis:• Mesolimbic system important for reinforcement of
behavior• We all have irrational thoughts, but usually brush
them aside• But if mesolimbic system was active when the
thought occurred, we might take it more seriously, leading to delusions
– Hypothesis cont.:• Confirming piece of evidence:
schizophrenics often report euphoria at onset of positive symptoms
• Disordered thinking?– System so active that it does not discriminate
between thoughts, making it hard to follow a logical sequence
• Terrifying element of delusions?– Strong dopaminergic projection to amygdala
Dopamine HypothesisEvidence for excessive dopamine
• Dopamine agonists (cocaine, amphetamine, PCP) produce symptoms of psychosis.
• Dopamine antagonists reduce psychotic behavior.
• Patients may have abnormalities involving dopamine autoreceptors.
SchizophreniaPositive Symptoms
• Schizophrenia– Positive Symptoms
– Chlorpromazine:• A “typical neuroleptic”
• A dopamine receptor blocker for D2 receptors
– Clozapine:• An “atypical neuroleptic”
• An antipsychotic drug that blocks D4 receptors in the nucleus accumbens
• Tardive dyskinesia involves tremors and involuntary movements.
• Supersensitivity: increased sensitivity of neurotransmitter receptors (D2) to dopamine
• Due to side effects, about 50% now use atypical neuroleptics like clozapine.
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SchizophreniaSide Effects of Typical Antipsychotics
SchizophreniaSide Effects of Typical Antipsychotics
Dopamine HypothesisEvidence for increase in D3 receptors
Failure of Prepulse Inhibition in Schizophrenia
Restoring Prepulse Inhibition in Schizophrenia
Problems With a Excessive Dopamine Hypothesis• 25% of patients do not respond to dopamine
antagonists.
• Atypical antipsychotic medications (clozapine) act primarily on neurotransmitters other than dopamine.
• Drugs change dopamine activity immediately, but patient may not improve for weeks.
• PCP produces symptoms similar to schizophrenia by blocking the NMDA glutamate receptor.
• Schizophrenia–Negative symptoms
–Brain damage:• Many of the negative symptoms are
also seen in people with frontal lobe damage
Lifetime risks of developing schizophrenia
Search for Brain AbnormalitiesEvidence for changes in ventricular size
Courtesy D.R. Weinberger, NIMH, St. Elizabeth’s Hospital, Washington, D.C.
Disorganization of cells in the hippocampus
Search for Brain AbnormalitiesLoss of gray matter with age
Search for Brain AbnormalitiesLoss of gray matter with age
Cause of delay of onset??
• Lower frontal lobe activity may account for the negative symptoms of schizophrenia.
• During rest (top) and an effortful cognitive test (bottom), patients with schizophrenia show less frontal lobe activity.
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Hypofrontality in schizophrenia
Hypofrontality in schizophreniaWisconsin Card Sorting Task
Possible Causes of the Brain Abnormalities
– Seasonal effect– Latitude effect– Maternal exposure to viruses– Nutritional deficiency
• Hunger Winter study– Thiamine deficiency– Vitamin D deficiency (latitude effect?)
– Father’s age– Rh Incompatibility
How are positive & negative symptoms related?
VTA
PrefrontalCortex
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DopamineHypoactivity(too little DA)
GABA neurons
Dopamine hyperactivity(too much DA)
18.17 Schematic representation of the neurodevelopmental model of schizophrenia
18.16 A modified representation of the vulnerability–stress model