Reduction of NMDA-induced Ca2+ transients by a mu-opioid receptor agonist in dorsal horn neurons.

Abstract

The effect of DAMGO, a mu-opioid receptor agonist, on intracellular Ca2+ transients evoked by the application of NMDA, was studied in freshly dissociated neurons from the superficial dorsal horn in the spinal cord of young rats. DAMGO (5-10 microns) reduced the amplitude of the Ca2+ transients measured with Fura-2 to 58 +/- 17% of the controls in 41% of the neurons tested. The effect of DAMGO was dose dependent and reversible. The reduction of NMDA-induced Ca2+ transients by DAMGO was prevented by application of the opioid antagonists naloxone (0.1-5 microM) and CTAP (0.2-2 microM). DAMGO also reduced Ca2+ transients induced by high K+ in 29% of the neurons. These data suggest that mu-receptor activation regulates NMDA-induced Ca2+ transients in a complex manner, by reducing both a depolarization-induced component and the NMDA-channel component of this Ca2+ signal.