Cortical opioid markers in schizophrenia and across postnatal development

Area of Science:

• Neuroscience
• Psychiatry
• Neurodevelopment

Background:

• Cognitive deficits in schizophrenia are associated with prefrontal cortical (PFC) GABA neuron dysfunction.
• Opioids are known to suppress GABA neuron activity, suggesting a potential link to schizophrenia pathophysiology.

Purpose of the Study:

• To investigate alterations in μ opioid receptor (MOR), δ opioid receptor (DOR), and proenkephalin mRNA in the PFC of schizophrenia subjects.
• To examine the postnatal developmental trajectory of altered opioid markers in the monkey PFC.

Main Methods:

• Quantitative polymerase chain reaction (qPCR) was used to measure mRNA levels.
• Human subjects included 42 schizophrenia patients and 42 matched controls.
• Non-human primate studies involved 18 monkeys with drug exposure and 49 across a wide age range (1 week-11.5 years).

Main Results:

• Schizophrenia subjects exhibited significantly higher MOR mRNA levels (+27%) in the PFC.
• No significant differences were found in DOR or proenkephalin mRNA levels.
• MOR mRNA levels in monkey PFC showed a developmental decline, stabilization before adolescence, and an increase in adulthood.

Conclusions:

• Elevated MOR mRNA in schizophrenia may contribute to suppressed PFC GABA neuron activity.
• These findings suggest that altered MOR signaling during early development could play a role in schizophrenia.
• The observed MOR alterations are unlikely explained by substance abuse, medication, or illness duration.