Quantitative assessment of jumping behaviour of morphine-like analgesics in mice.

The withdrawal jumping behaviour under the influence of twelve narcotic analgesics was compared in order to estimate the degree of morphine-like physical dependence in mice. The vertical jumping was elicited by an intraperitoneal injection of nalorphine followed by seven subcutaneous administrations of each drug studied during two days. During the 30 min of the observation period, the number and the height of jumps as well as the distribution of jumps were recorded. The jumping rate of the mice due to the drugs was nearly dose-dependent. The mice injected with morphine or levorphanol exhibited a large number of high jumps mostly during the first 10 min, with a maximal incidence of jumping. Mice injected with drugs inducing a low or moderate degree of physical dependence such as codeine exhibited low and few jumps, a maximal incidence being observed with codeine, whereas the incidence with pentazocine and nalorphine amounted to only 20% or less. Levorphanol exhibited the lowest JD50 (median effective dose required to produce jumping) and the JD50 of morphine was about one-tenth that of codeine. The potential rank order of the drugs as to jumping activity roughly corresponded with that of their morphine-like physical dependence inducing effect in man. Of eighteen non-narcotic drugs tested, only apomorphine possessed a jumping activity. However, the jumping behaviour with apomorphine was dissimilar to that with morphine-like analgesics. From these results, it can be suggested that this method to observe the jumping behaviour is suitable to evaluate the degree and property of morphine-like physical dependence in mice.