Morphine inhibits Purkinje cell survival and dendritic differentiation in organotypic cultures of the mouse cerebellum

The effects of morphine on the morphogenesis and survival of calbindin-D(28k)-immunoreactive Purkinje cells were studied in organotypic explant cultures isolated from 1- or 7-day-old mouse cerebella. To reduce experimental variability, bilaterally matched pairs of organotypic cultures were used to compare the effects of opiate drug treatment. One explant within each pair was untreated, while the remaining explant was continuously treated for 7 to 10 days with morphine, morphine plus naloxone, or naloxone alone. In explants derived from 1-day-old mice, morphine treatment significantly reduced Purkinje cell dendritic length compared to symmetrically matched untreated control explants. The concentration of morphine estimated to cause a half-maximal reduction (EC₅₀) in dendritic length was 4.9 x 10^-8 M. At higher concentrations (EC₅₀ = 3.6 x 10^-6M), morphine also significantly decreased the number of Purkinje cells in explants from 1-day old mice compared to untreated explants. Electron microscopy identified increased numbers of degenerating Purkinje cells in explants derived from 1-day-old mice. This showed that high concentrations (10^-5M) of morphine reduced Purkinje cell numbers by decreasing their rate of survival. In explants derived from 7-day-old mice, morphine (10^-5 M) neither affected Purkinje cell dendritic length nor cell numbers compared to symmetrically matched untreated (control) explants. Collectively, these findings suggest that morphine per se, through a direct action on the cerebellum, can affect Purkinje cell differentiation and survival. The results additionally suggest that there is a critical period during development when Purkinje cells are especially vulnerable to the effects of morphine.