Abstract
The effects of μ‐agonists (morphine, fentanyl) andx‐agonists (U‐50,488, U‐69,593, bremazocine, nalbuphine, tifluadom) on the electroconvulsive threshold were studied in mice. The threshold could be significantly elevated by all drugs tested in a dose range that was in the order of magnitude of the antinociceptive ED50. Mice tolerant to the antielectroshock effect of morphine still reacted to U‐69,593. The antagonism of the anticonvulsant effect by the μ‐antagonist naloxone and thex‐antagonist MR 2266 was receptor‐specific only with fentanyl and U‐50,488. The other opioid agonists were either antagonized by both drugs (morphine, U‐69,593, bremazocine, nalbuphine) or even by the opposite antagonist (tifluadom). A synergistic effect of μ‐ andx‐stimulation is assumed for the mediation of the antielectroshock effect of opioid drugs, but drugs with high affinity and intrinsic activity at one receptor type (fentanyl, U‐50,488) are obviously able to bring about their antielectroshock effect through the one respective opioid binding site.