dopamine hypothesis. learning objectives by the end of the lesson your goal is to be able to...
TRANSCRIPT
DOPAMINE HYPOTHESIS
LEARNING OBJECTIVES
By the end of the lesson your goal is to be able to
• DescribeDescribe the role of Dopamine (DA) in schizophrenia
and you should be able to• OutlineOutline evidence to support this
hypothesisYou could even be able to• EvaluateEvaluate the Dopamine Hypothesis
Lets remind ourselves how neurotransmitters work
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Lets remind ourselves how neurotransmitters work
DOPAMINE HYPOTHESIS
The Dopamine hypothesis states that the brain of schizophrenic patients produces
moremore dopamine than normal brains.
Evidence for this comes from
studies with drugs
post mortems
pet scans
Dopamine Hypothesis
Although the original Dopamine Hypothesis states that the brain of schizophrenic patients produces more dopamine than the brain of a “normal” person.
It is now thought that schizophrenics have an abnormally high number of D2 receptors.
Normal Level of Dopamine In The
Human Brain
Elevated Level of Dopamine In The Brain of a Schizophrenic Patient
(specifically the D2 receptor)
Neurons that use the transmitter ‘dopamine’ fire too often and transmit too many messages.
There may be an excess of DA receptors at the synapse in schizophrenics
Lowering DA activity helps remove the symptoms of schizophrenia
ROLE OF DRUGS
Amphetamines (agonists – prevent the breakdown of dopamine) lead to increase in DA levels
Large quantities lead to delusions and hallucinations
If these drugs are given to schizophrenic patients their symptoms get worse
Randrup et al
Rats given amphetamines developed schizophrenia type symptoms
Parkinson’s disease
• Parkinson’s sufferers have low levels of dopamine
• L-dopa raises DA activity • People with Parkinson's develop
schizophrenic symptoms if they take too much L-dopa
–Chlorphromazine (given to schizophrenics) reduces the symptoms by blocking D2 receptors
Seidman (1990)Post-mortem (after death) examinations have found
that people with schizophrenia have a larger than usual number of dopamine receptors.
Increase of DA in brain structures and receptor density (left amygdala and caudate nucleus putamen)
Concluded that DA production is abnormal for schizophrenia
What is a strength and weakness of a post-mortem study?
Post-mortems
Lindstroem et al (1999)• Radioactively labelled a chemical L-Dopa • administered to 10 patients with
schizophrenia and 10 with no diagnosis• L-Dopa taken up quicker with
schizophrenic patients• Suggests they were producing more DA
than the control group
PET SCANS
Gjedde and Wong (1987)There are more than twice as many
dopamine receptors in schizophrenics compared to controls.
Farde et al. (1990)There is no difference in the number of
dopamine receptors between schizophrenics and controls.
PET Scans
What is the main strength of a PET scan?
What conclusions can be drawn from the research findings?
Schizophrenia or Faulty Chemicals?
Faulty chemicals cause schizophrenia but
schizophrenia may cause faulty chemicals
Chickens hatch from
eggs, but a mother chicken
must keep an
egg warm in order for
it to hatch
The Chicken or the Egg?
Which Came First?
Drugs may influence other systems that impact on schizophrenia so we cannot be 100% sure about their effects
There are lots of problems with the dopamine hypothesis!
• Read your handout / pg 248-250 in Brain carefully.
• There is a lack of correspondence between taking phenothiazines and signs of clinical effectiveness. It takes 4 weeks to see any sign that the drugs are working when they begin to block dopamine immediately. We cannot seem to explain this time difference.
• It could be that the development of receptors in one part of the brain may inhibit their development in another.
Other EVALUATION POINTS
• Type 1 cases respond well to conventional anti-psychotic drugs. Drugs such as CHLOPROMAZINE: Only effective at relieving the Positive Symptoms of the Illness.
• Not good at explaining negative symptoms. Therefore suggested that Type 2 is related to a different kind of abnormality such as brain structure.
• PET scans have suggested that drugs did not reduce symptoms of patients diagnosed with disorder for 10 yrs or more
• There may be other neurotransmitters involved.
• Possible that social and environmental factors trigger the condition.
ACTIVITY• Describe and evaluate the dopamine Describe and evaluate the dopamine
hypothesis as an explanation of hypothesis as an explanation of schizophrenia schizophrenia
•You must comment on how the evidence you use supports or challenges the DA hypothesis.
• You should comment on evidence both for and against the hypothesis.
• You could use your own skills and knowledge to make additional critical and evaluative points.