Neurotransmitters (biological explanation) of schizophrenia Flashcards
(20 cards)
What is dopamine?
Functions as a neurotransmitter -chemical released by neurons to send signals to other neurons
Brain includes several dopamine pathways
What is the transmission process?
- Action potential fires a signal to release neurotransmitter into pre synaptic neuron
- Fusion = Neurotransmitters are released into synaptic gap
- Receptors pick up the neurotransmitters
- If receptors are full or dont fit into NTs, NTs dissolve or reuptake by vesicles which hold + release them when needed
What is the dopamine hypothesis?
Suggests that an excess of dopamine may be responsible for schizophrenia
Why would someone have excess dopamine levels?
- May have excess dopamine receptors
- Exercise
- Recreational drugs, alcohol
- Addiction = Increased dopamine desensitises us + we become addicted to dopamine
Explain hyperdopaminergia:
Extra dopamine
In 50s, 2 antipsychotic drugs found to help reduce symptoms of schizophrenia
However, both caused tremors + muscle rigidity (symptoms of parkinsons - caused by low dopamine). Therefore argued that schizophrenia caused by high dopamine levels
What are the 2 explanations for high levels of dopamine? (hyperdopaminergia)
- Low levels of beta hydroxylase, enzyme which breaks down dopamine. So excess dopamine left behind
- Certain dopamine receptors (D2 receptors) may be hypersensitive to presence of neurotransmitter/theres more D2 receptors on postsynaptic cells
Explain hypodopaminergia (dopamine deficiency):
Positive symptoms (excess) due to excess dopamine in mesolimbic pathway
Negative symptoms (lack of) may be caused by lack of dopaminergic activity in mesocortical pathway
What is the function of the mesocortical pathway?
Cognition, movement
Goes to prefrontal cortex - explains emotional flatness due to low dopamine
How does irregular serotonergic activity cause schizophrenia?
Clozapine (antipsychotic drugs found) binds to D1 + D2 dopamine receptors, + only weakly binds to D2 receptors
Clozapine binds to serotonin receptors + reduces both positive + negative symptoms
However, serotonin does regulate dopamine levels in places like mesolimbic pathway
How do we know that mesolimbic pathway is positive and mesocortical pathway is negative?
Evidence comes from PET scans + animal studies
What is the function of glutamate?
Controls memory + learning, neural processing, + brain development by binding to glutamate receptors (e.g. NMDA)
These receptors found everywhere in brain, so important for glutamate levels to be low by healthy glutamate uptake
What is the glutamate hypothesis of schizophrenia?
Proposed based on observation that NMDA antagonists (blocks something) induced positive + negative symptoms in healthy individuals that resembled schizophrenia
What do animal studies show about being treated with an NMDA antagonist?
Led to lack of glutamate but not always an increase in dopamine
If NMDA antagonists lead to psychosis-like symptoms + inhibit dopamine release, this doesnt support idea that excess dopamine causes schizophrenia
What may also contribute to schizophrenia?
Glutamate deficiencies
What is an example of an NMDA antagonist?
PCP (angel dust), led to lower glutamate levels + higher dopamine
Glutamate receptor antagonists can counteract affects of PCP even if dopamine high - suggests dopamine alone cant cause schizophrenia + other NTs play a part
What may a lack of glutamate in schizophrenics explain?
Having difficulty with sustaining attention, cognitive control, + working memory
What might glutamate failure in the cerebral cortex cause?
Negative symptoms
What might glutamate failure in basal ganglia lead to?
Positive symptoms
What was discovered about serotonin?
Recent antipsychotics targetting serotonin as well as dopamine have been effective in treating schizophrenia, especially negative symptoms However
Suggests serotonin plays a role in illness
How is GABA involved in schizophrenia?
Ppl with schizophrenia have low levels of GABA (calming NT)
Lower the levels, more serious the symptoms
