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Lack of mu-opioid receptor leads to an increase in the NMDA receptor subunit mRNA expression and NMDA-induced

C G Jang1, S Y Lee, H H Loh

  • 1Department of Pharmacology, College of Pharmacy, Sungkyunkwan University, 440-746, Suwon, South Korea.

Brain Research. Molecular Brain Research
|October 13, 2001
PubMed

Insights

Mu-opioid receptor knockout mice exhibit heightened sensitivity to N-methyl-D-aspartate (NMDA) induced seizures. This suggests that the absence of the mu-opioid receptor gene alters the NMDA receptor system, impacting synaptic excitability and potentially influencing conditions like epilepsy.

Area of Science:

  • Neuroscience
  • Pharmacology
  • Genetics

Background:

  • The mu-opioid receptor system plays a role in modulating neuronal excitability.
  • N-methyl-D-aspartate (NMDA) receptors are critical ionotropic glutamate receptors involved in synaptic plasticity and excitability.
  • Understanding the interplay between opioid receptors and NMDA receptors is crucial for neurological research.

Purpose of the Study:

  • To investigate the functional changes in the NMDA receptor system in mu-opioid receptor gene knockout mice.
  • To determine if the absence of mu-opioid receptors affects susceptibility to NMDA-induced convulsions.

Main Methods:

  • In situ hybridization was used to quantify NMDA receptor subunit mRNA levels in specific brain regions of knockout and wild-type mice.
  • Intracerebroventricular injection of NMDA was employed to induce convulsions, and dose-response relationships (ED50) were determined.

Main Results:

  • Mu-opioid receptor knockout mice showed significant increases in NR1, NR2A, and NR2B subunit mRNA levels in various brain regions, including the parietal cortex, thalamus, and hypothalamus.
  • The ED50 for NMDA-induced convulsions was significantly lower in knockout mice compared to wild-type mice, indicating increased sensitivity.
  • Potency ratio analysis confirmed a 1.44-fold higher sensitivity to NMDA-induced convulsions in mu-opioid receptor knockout mice (P < 0.05).

Conclusions:

  • The absence of the mu-opioid receptor gene is associated with alterations in the NMDA receptor system.
  • These changes in the NMDA receptor system in knockout mice lead to increased sensitivity to NMDA-induced convulsions.
  • The findings suggest a modulatory role of the mu-opioid receptor system on NMDA receptor function, impacting synaptic excitability relevant to conditions like epilepsy.

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