💗 Schizophrenia Biological Explanation - Dopamine Hypothesis Flashcards
(19 cards)
What is the main neurotransmitter involved in the dopamine hypothesis?
Dopamine
Dopamine regulates mood, attention, and is crucial in the reward system of the brain.
What does the Dopamine hypothesis propose about schizophrenic patients?
Greater dopamine activity in the brain
This may be due to increased dopamine production, greater receptor sensitivity, or more dopamine in the synaptic gap.
Who supported the initial dopamine hypothesis and how?
J.J. Griffith (1968) induced psychosis in non-schizophrenics with dextro-amphetamine
Volunteers exhibited abrupt paranoid delusions and emotional detachment.
What limitation was found in the initial dopamine hypothesis?
Drugs reducing dopamine levels had little effect on negative symptoms
This indicated that the hypothesis was too simplistic.
What are the three sources of evidence for the dopamine hypothesis?
- Studies with drugs
- Post mortem analyses
- PET scans
These sources help in understanding dopamine’s role in schizophrenia.
What are the subtypes of dopamine receptor sites mentioned in the text?
D1-D5
These receptors are located in the cerebral cortex and under the cortex in limbic system.
What role does the D2 receptor play in the brain?
Inhibits neuronal excitability
D2 receptors are primarily found in subcortical regions. This made the limbic system the main focus of the domaine hypothesis.
What is the focus of the revised dopamine hypothesis?
The role of dopamine in the limbic system
The limbic system is involved in emotions, memory, and arousal.
Nerve pathways leave the limbic system to many areas such as the cerebral cortex
What are the two key pathways associated with schizophrenia?
- Mesolimbic pathway
- Mesocortical pathway
These pathways are linked to positive (Mesolimbic) and negative (mesocortical) symptoms of schizophrenia.
What is the function of the mesolimbic pathway?
Carries signals from the ventral tegmental area to the nucleus accumbens
Overstimulation in this pathway leads to positive symptoms like hallucinations.
Dompamine is the major neurotransmitter here.
How do antipsychotic drugs affect the mesolimbic pathway?
They reduce dopamine transmission
This reduction helps alleviate positive symptoms in schizophrenia patients.
What is the function of the mesocortical pathway?
Carries signals from the ventral tegmental area to the frontal lobe
This pathway is crucial for emotional responses, motivation, and cognition.
Too little DA in the D1 receptors of the frontal lobe is linked with negative symptoms and cognitive impairments.
What do conventional (typical) antipsychotics do?
Block dopamine neurotransmission
This action helps in managing symptoms of schizophrenia.
What distinguishes atypical antipsychotics from conventional antipsychotics?
Atypical antipsychotics affect other neurotransmitters like serotonin
They primarily target dopamine neurotransmission but have broader effects.
Evaluation: Genetic Basis of Dopamine Imbalances
Q: How does genetic evidence support the dopamine hypothesis?
- Gottesman et al. (1991): Twin/family studies show schizophrenia risk increases with genetic similarity.
- Psychiatric Genomics Consortium (2014): Identified 108 genetic loci linked to schizophrenia.
- Implication: Supports genetic predisposition but no single “schizophrenia gene.” Dopamine imbalances may be one component of a complex genetic picture.
Evaluation: Limitations of Genetic Evidence
Q: What are the weaknesses of genetic support for the dopamine hypothesis?
- No single gene directly causes schizophrenia.
- Over 100 loci involved → suggests multiple factors (genetic + environmental) beyond dopamine.
- Link: Dopamine is just one piece; other neurobiological/environmental influences matter.
Evaluation: Measuring Dopamine Metabolites
Q: How do researchers study dopamine in schizophrenia, and what are the limitations?
- Method: Measure HVA (dopamine metabolite) in cerebrospinal fluid via spinal tap.
- Problem: Indirect and unreliable; HVA levels influenced by non-dopamine factors.
- Evaluation: Still useful but requires cautious interpretation until better methods exist.
Evaluation: Serotonin’s Role (Challenge to Dopamine Hypothesis)
Q: How does serotonin complicate the dopamine hypothesis?
- Evidence: Atypical antipsychotics (e.g., clozapine) block D2 (dopamine) AND 5-HT2A (serotonin) receptors.
- Implication: Schizophrenia involves multiple neurotransmitters; dopamine alone is insufficient to explain symptoms.
- Evaluation: Doesn’t disprove dopamine’s role but supports a multi-neurotransmitter model.
Evaluation: Cause vs. Effect Problem
Q: Why is it unclear if dopamine causes schizophrenia or vice versa?
- PET scan studies (e.g., Goodwin & Crook, 2000): Can’t determine if dopamine abnormalities are a cause or consequence of schizophrenia.
- Implication: If dopamine dysfunction is secondary, targeting it may not address root causes.
- Evaluation: Dopamine still matters for symptoms/treatment, but origins likely involve other factors.
