PMID: 9190856Jun 1, 1997Paper

Spinal infusion of N-methyl-D-aspartate antagonist MK801 induces hypersensitivity to the spinal alpha-2 agonist ST91 in the rat

The Journal of Pharmacology and Experimental Therapeutics
S Dunbar, T L Yaksh

Abstract

MK801 (MK), an N-methyl-D-aspartate (NMDA) receptor antagonist, attenuates tolerance to spinal opioids. Whether this applies to other G-protein-coupled receptor systems is unknown. This study examines the effects of continuous spinal MK on tolerance to the antinociceptive effect of continuous spinal infusion of the alpha-2 agonist ST91 (ST). Intrathecal (i.t.) infusion pumps were implanted in rats which delivered for 7 days: saline (1 microl/h); ST (40 nmol/microl/h); MK (10 nmol/microl/h) + ST (40 nmol/microl/h); or MK (10 nmol/microl/h). Antinociception was measured daily on the hot plate. On day 8, groups received i.t. boluses of ST to generate dose-response curves. A separate ST-infused group received MK (10 nmol i.t.) on day 7. Each group received ST (40 nmol i.t.) 7 days after discontinuation of infusion. Co-infusion of MK with ST resulted in attenuation of the right shift in dose response seen in ST-infused rats and a small preservation of effect on daily testing. However, MK-infused rats showed a significant left shift in ST dose response. Acutely administered, MK did not restore ST sensitivity. One week after cessation of infusion, ST and ST + MK groups showed shorter duration of effect after i.t. ST bolus than control...Continue Reading

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