Stereospecific accumulation of dihydromorphine and naltrexone by corpus striatal slices of morphine-dependent mice.

Stereospecific accumulation of [3H]dihydromorphine and [3H]naltrexone by striatal slices from morphine-dependent mice was examined in Krebs-Ringer bicarbonate medium. Striatal slices showed a saturable and stereospecific accumulation of both [3H]ligands. The accumulation constant of naltrexone, determined by Wilkinson's analysis, was significantly decreased in both morphine-dependent mice and dependent mice abruptly withdrawn for 6 hr. The maximal accumulation of naltrexone was not changed in withdrawn mice, but decreased in dependent mice. This could be due to the high concentration of residual morphine in the slices. There were no significant differences in the accumulation constant or maximal accumulation of dihydromorphine among the striatal slices from control, dependent and withdrawn mice. These data indicate that in morphine-dependent mice, there is an increased affinity of the opioid receptors for the narcotic antagonist, naltrexone but not for the agonist, dihydromorphine.