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Eur J Pharmacol. 1993 Nov 30;250(1):R7-8.

Functional antagonism of morphine analgesia by (+)-pentazocine: evidence for an anti-opioid sigma 1 system.

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Cotzias Laboratory of Neuro-Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021.


Both (+)-pentazocine and (-)-pentazocine antagonize morphine analgesia equally well. This lack of stereospecificity implies an non-opioid mechanism of action. The antagonism of morphine analgesia by (+)-pentazocine is reversed by haloperidol, a potent dopamine D2 and sigma receptor antagonist. The inactivity of the highly selective dopamine D2 receptor antagonist (-)-sulpiride indicates that both (+)-pentazocine and haloperidol are acting through sigma receptors. Haloperidol, but not (-)-sulpiride, also enhances morphine analgesia. Together, these results suggest the presence of a tonically active anti-opioid sigma system within the brain.

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