Which neurotransmitter hypothesis is most strongly supported in the pathophysiology of schizophrenia?

Explanation

## Dopamine Hypothesis of Schizophrenia **Key Point:** The dopamine hypothesis remains the most robust neurochemical model of schizophrenia, supported by the mechanism of action of all antipsychotic medications and neuroimaging evidence. ### The Dopamine Dysregulation Model **Mnemonic: MESO** — Mesolimbic (hyperactive), Mesocortical (hypoactive) #### Mesolimbic Pathway (Hyperactive) - **Location:** Ventral tegmental area (VTA) → nucleus accumbens and limbic structures - **Result:** Excessive dopamine activity - **Clinical correlate:** Positive symptoms (hallucinations, delusions, disorganized behavior) - **Mechanism:** Overactivity in reward and emotion processing circuits #### Mesocortical Pathway (Hypoactive) - **Location:** VTA → prefrontal cortex (PFC) - **Result:** Insufficient dopamine activity - **Clinical correlate:** Negative symptoms (alogia, avolition, affective flattening) and cognitive deficits - **Mechanism:** Reduced executive function, motivation, and emotional expression ### Evidence Supporting This Model 1. **Antipsychotic mechanism:** All antipsychotics block D~2~ dopamine receptors, reducing mesolimbic hyperactivity 2. **Amphetamine psychosis:** Stimulants (which increase dopamine) can precipitate psychotic symptoms in vulnerable individuals 3. **PET/SPECT imaging:** Shows elevated dopamine synthesis capacity in striatum of untreated patients 4. **Medication response:** Correlates with D~2~ receptor occupancy (60–70% occupancy = clinical response) ### Limitations of the Dopamine Hypothesis - Does not fully explain negative symptoms or cognitive deficits - Does not account for glutamate and other neurotransmitter abnormalities - Does not explain why some patients are treatment-resistant **Clinical Pearl:** The dopamine hypothesis explains why antipsychotics work but does not explain why schizophrenia develops. Modern understanding incorporates glutamate dysregulation, neuroinflammation, and genetic factors. **High-Yield:** For NEET PG, remember: dopamine hyperactivity → positive symptoms; dopamine hypoactivity in PFC → negative symptoms and cognitive deficits. This is tested frequently in pharmacology and pathophysiology sections.