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 expla nt cultures isolated from 1- or 7-day-old mouse cerebella. To reduce e xperimental variability, bilaterally matched pairs of organotypic cult ures were used to compare the effects of opiate drug treatment. One ex plant within each pair was untreated, while the remaining explant was continuously treated for 7 to 10 days with morphine, morphine plus nal oxone, or naloxone alone. In explants derived from 1-day-old mice, mor phine treatment significantly reduced Purkinje cell dendritic length c ompared to symmetrically matched untreated control explants. The conce ntration of morphine estimated to cause a half-maximal reduction (EC(5 0)) in dendritic length was 4.9 x 10(-8) M. At higher concentrations ( EC(50) = 3.6 X 10(-6) M), morphine also significantly decreased the nu mber of Purkinje cells in explants from 1-day-old mice compared to unt reated explants. Electron microscopy identified increased numbers of d egenerating Purkinje cells in explants derived from 1-day-old mice. Th is showed that high concentrations (10(-5) M) of morphine reduced Purk inje cell numbers by decreasing their rate of survival. In explants de rived from 7-day-old mice, morphine (10(-5) M) neither affected Purkin je cell dendritic length nor cell numbers compared to symmetrically ma tched untreated (control) explants. Collectively, these findings sugge st that morphine per se, through a direct action on the cerebellum, ca n affect Purkinje cell differentiation and survival. The results addit ionally suggest that there is a critical period during development whe n Purkinje cells are especially vulnerable to the effects of morphine. (C) 1994 Academic Press, Inc.