Overview of Psychotic Symptoms and Theories of Psychosis

Focus of Lecture

• Overview of psychotic symptoms and theories related to psychosis
• Main focus: Dopamine and its role in schizophrenia

Psychosis

• Definition: A syndrome with mixed symptoms; not a specific disorder
• Key Symptoms:
  • Delusions: Fixed, often bizarre beliefs not altered by evidence
  • Hallucinations: Perceptual experiences without external stimuli; vivid and clear
• Positive Symptoms: Delusions, hallucinations, disorganized speech/behavior, reality distortion
• Negative Symptoms: Diminished emotional expression, decreased motivation

Schizophrenia

• Used as a prototype for understanding psychosis
• Symptoms:
  • Positive: Delusions, hallucinations, disorganized speech/behavior
  • Negative: Apathy, anhedonia, cognitive blunting, neuroleptic dysphoria

Brain Regions and Circuits

• Different symptoms linked to different brain circuits
  • Mesolimbic Area: Positive symptoms
  • Mesocortical and Prefrontal Cortex: Negative symptoms
  • Nucleus Accumbens: Reward circuitry
  • Orbital Frontal Cortex & Amygdala: Aggressive/impulsive symptoms

Dopamine and Psychosis

• Dopamine Hypothesis: An enduring idea in understanding psychosis
• Other Neurotransmitters: Glutamate and serotonin are also implicated
• Theories:
  • Dopamine Theory: Excess dopamine at D2 receptors in mesolimbic pathway
  • Glutamate Theory: NMDA receptor hypofunctioning
  • Serotonin Theory: Hyperfunctioning of 5HT2A receptors in cortex

Dopamine Pathways

• Five Major Pathways:
  • Mesolimbic: Emotional behaviors, reward; linked to positive symptoms
  • Mesocortical: Cognition, executive functioning, emotional regulation
  • Nigrostriatal: Motor movements
  • Tuberoinfundibular: Prolactin regulation
  • Others: Still under research, possibly involved in sleep/arousal

Dopamine Synthesis and Function

• Process:
  • Starts with amino acid tyrosine
  • Converted to dopamine via enzymes (TOH, DDC)
  • Stored in vesicles for neurotransmission
• Handling Excess Dopamine:
  • Reuptake and recycling
  • Breakdown by enzymes (COMT, MAOA/B)
  • Transported via norepinephrine transporter

Dopamine Receptors

• Types:
  • D1-like: D1 and D5, excitatory
  • D2-like: D2, D3, D4, inhibitory
• Role:
  • Regulate neurotransmission
  • Found pre and post-synaptically

Treatment Implications

• Medications affect all dopamine pathways
• Side effects arise from lack of pathway selectivity
• Importance of understanding pathways to manage schizophrenia symptoms and treatment side effects

Conclusion

• Dopamine’s role is significant in psychosis and schizophrenia
• New findings suggest mesostriatal involvement in emotional regulation
• Ongoing research to fully understand neurotransmitter interactions and their implications in psychosis