Comparison of the effects of morphine on locomotor activity, analgesia and primary and protracted physical dependence in six mouse strains.

Mice of the DBA/2J, A/J, C3H, C57BL/L, ICR and Swiss strains were studied with respect to acute and chronic morphine administration. The acute administration of morphine resulted in a dose-dependent running response in C57BL/6, C3H, ICR and Swiss strains, but no running response in DBA/2J and A/J strains. Strain differences in sensitivity to morphine-induced running activity did not parallel differences in sensitivity to morphine-induced running activity did not parallel differences in sensitivity to antinociception in the abdominal constriction test (r = 0.404), but significantly correlated with differences in the expression of physical dependence as measured by either precipitated (r = 0.957) or abrupt (r = 0.927) withdrawal jumping behavior in mice made dependent by morphine pellent implantation. Mortality for 3 days of pellet implantation ranged from 5% in ICR mice to 84% in A/J mice. Strain differences in degree of initial physical dependence. These results suggest the possibility that the running response and withdrawal jumping may involve at least part of the same neuronal pathway. This pathway may include dopamine-containing neurons which terminate in the neostriatum.