An evaluation of the analgesia induced by morphine gamma-hydroxybutyrate.

Experiments were performed to determine 1) whether synergism existed between morphine and gamma-hydroxybutyrate in the production of analgesia and 2) the effect of each of these agents on pain-induced changes in brain amino acid content in mice. The analgetic ED50 for both agents was determined using hot plate and tail-flick procedures. The combination of one-half the ED50 of each agent produced an effect equivalent to the ED50 of either agent administered alone in the hot plate but not in the tail-flick test. Although both agents produced an unresponsiveness to noxious stimulation, only morphine prevented pain-induced alterations in brain GABA and glutamate levels.