[The characteristics of the effects of morphine and naloxone in rat strains differing by the excitability thresholds of their nervous systems].

Effect of morphine and naloxone on nociceptive sensitivity were studied in 3 rat strains, with high, low, and intermediate thresholds of nervous system excitability. The highest sensitivity to morphine correlated with its dose dependence was revealed in rats with low and high thresholds of excitability. The lowest sensitivity was found in rats with intermediate thresholds of excitability. The obtained data led to the conclusion about essential contribution of genetical control of excitability in the mechanisms of functioning of the opiate system.