Biological explanations Flashcards
Outline the dopamine hypothesis.
Dopamine is one of the many different neurotransmitters that operate in the brain. The Dopamine Hypothesis states that messages from neurons that transmit dopamine fire too easily or too often leading to the characteristic symptoms of schizophrenia. Schizophrenics are thought to have abnormally high levels of D2 receptors on receiving neurons resulting in more dopamine binding and thus more neurons firing.
What is the key role of dopamine?
Dopamine plays a key role in guiding attention so disturbances in this process may well lead to the problems related to attention, perception and thought found in people with Schizophrenia.
How is the role of dopamine highlighted by Amphetamines?
Amphetamine drugs are dopamine agonists and increase levels of dopamine in the synapses. Large amounts of Amphetamines can cause the characteristic symptoms of Schizophrenia such as Hallucinations and delusions.
How is the role of dopamine highlighted by Anti-Psychotic Drugs?
Although there are many different types of antipsychotic drugs; they all have one thing in common – they look to block dopamine activity in the brain.
How is the role of dopamine highlighted by Parkinson’s Disease?
Low levels of Dopamine are found in those suffering from Parkinson’s disease. Drugs taken to increase this resulted in such individuals developing Schizophrenic symptoms highlighting a link between excess dopamine and Schizophrenia.
What did Davis do?
Davis updated the original theory arguing it to be too reductionist and simplistic because high levels of dopamine were not found in all schizophrenics and modern anti-psychotic drugs such as Clozapine work effectively against the disorder yet have very little dopamine blocking activity.
What do the new theories suggest?
New theories suggest high levels of dopamine in the Mesolimbic dopamine system are associated with positive symptoms of schizophrenia while high amounts in the Mesocortical system are associated with negative symptoms.
What does other research focus on (apart from the dopamine hypothesis)?
Other research has focused on the neurotransmitter Glutamate as reduced function of the NMDA Glutamate receptor is found in Schizophrenics. Glutamate release is inhibited by Dopamine receptors and it may be the two are involved and not necessarily Dopamine alone.
What did Iverson find?
Iverson reported post-mortems on Schizophrenics found excess levels of Dopamine in the limbic systems suggesting Dopamine to be involved in the disorder. However differences in biochemistry of Schizophrenics could just as easily be an effect rather than a cause of Schizophrenia.
What did Javitt find?
Javitt found that Glycine, a glutamate agonist reversed the symptoms of Schizophrenia is rats supporting the Glutamate Theory and its involvement with Schizophrenia suggesting Dopamine alone is not involved.
Criticism of Javitt’s study?
Studies with animals cannot be generalised to humans due to the huge difference in anatomy.
What did Healy argue?
Healy argued pharmaceutical companies were keen to see the Dopamine Theory promoted as it allowed them to make huge profits from manufacturing antipsychotic drugs that inhibit Dopamine for profit.
Explain the second generation atypical drugs.
Second generation Atypical drugs look to reduce serotonin as well as Dopamine and such drugs have found to be better in treating Schizophrenia compared to typical varieties suggesting dopamine alone is not the sole cause and other neurotransmitters and factors also need to be included.
What is the major problem with the dopamine hypothesis?
A major problem for the dopamine hypothesis is that drugs used to actually reduce dopamine levels can actually increase them as the body attempts to compensate for the sudden deficiency. Research in to post-mortems of schizophrenics has shown that those with elevated levels had taken antipsychotics just prior to death. Those with normal dopamine levels had not taken any medication and this goes against the Dopamine hypothesis.
Further problems with dopamine hypothesis?
Drugs designed to reduce dopamine levels work effectively after a few hours yet it takes many weeks for patients to have fewer schizophrenic symptoms. This suggests although dopamine may be involved; it may only be one of the many links in the chain that causes the disorder.
Neuroimaging and PET scans have allowed researchers to investigate dopamine activity more accurately than previous methods. However as of yet no link has been found to suggest excess dopamine activity in the brain occurred with Schizophrenics.
