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The NMDA receptor antagonist MK-801 increases morphine catalepsy and lethality
1Mental Health Research Institute, University of Michigan, Ann Arbor, MI 48109-0720.
Abstract:
Interactions between excitatory amino acids and opioids were examined by studying the ability of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 to affect morphine catalepsy and lethality. MK-801 (0.3 mg/kg) reduced the ED50 for morphine-induced catalepsy from approximately 30 mg/kg to less than 10 mg/kg, and reduced the LD50 for morphine from approximately 100 mg/kg to approximately 10 mg/kg. Lower doses of MK-801 did not affect morphine catalepsy or lethality. MK-801, in the absence of morphine, produced no catalepsy or lethality at doses up to 3.0 mg/kg; at 0.3 mg/kg MK-801 caused weaving, body rolling and ataxis, as previously described, while at 3.0 mg/kg animals appeared to lose muscle tone, becoming limp. These results demonstrate that blockade of NMDA receptors can dramatically potentiate morphine catalepsy and lethality, and suggest a potential dangerous interaction with opioids in the clinical use of NMDA receptor antagonists.
Insights
The NMDA receptor antagonist MK-801 significantly amplified morphine
Area of Science:
- Neuropharmacology
- Opioid Research
- Excitatory Amino Acid Signaling
Background:
- Opioids and excitatory amino acids interact in the central nervous system.
- N-methyl-D-aspartate (NMDA) receptors are key mediators of excitatory amino acid neurotransmission.
- Understanding these interactions is crucial for safe clinical practice.
Purpose of the Study:
- To investigate the interaction between NMDA receptor blockade and opioid effects.
- To determine if the NMDA receptor antagonist MK-801 potentiates morphine-induced catalepsy and lethality.
Main Methods:
- Administration of the NMDA receptor antagonist MK-801 at varying doses.
- Assessment of morphine's median effective dose (ED50) for catalepsy.
- Determination of morphine's median lethal dose (LD50).
- Observation of behavioral effects of MK-801 alone.
Main Results:
- A dose of 0.3 mg/kg MK-801 significantly reduced the ED50 for morphine catalepsy and the LD50 for morphine.
- Lower doses of MK-801 did not alter morphine's effects.
- MK-801 alone did not cause catalepsy or lethality at tested doses, but induced ataxia and muscle hypotonia at higher concentrations.
Conclusions:
- Blockade of NMDA receptors markedly potentiates morphine's cataleptic and lethal effects.
- Clinical use of NMDA receptor antagonists alongside opioids may pose significant risks.
- Further research into these interactions is warranted to ensure patient safety.