Perinatal exposure to morphine: reactive changes in the brain after 6-hydroxydopamine.

The effects of neonatal 6-hydroxydopamine treatment on the brain of control rats and of rats perinatally exposed to morphine were examined. Noradrenaline levels were increased in the pons-medulla, mesencephalon and caudate of 8-week-old control rats lesioned with neonatal 6-hydroxydopamine; perinatal morphine treatment prevented such an increase. In the caudate, there was a loss of dopamine and an increase of serotonin following the neurotoxic lesion; exposure to perinatal morphine prevented the serotonin increase. Brain expression of synapsin I mRNA was particularly abundant in cerebral cortex, hippocampus, dentate gyrus and olfactory bulb. In perinatal morphine-treated rats, the expression of synapsin I mRNA was significantly reduced; interestingly, the neonatal treatment with 6-hydroxydopamine normalized its expression. Therefore, brain-reactive neurochemical changes triggered by 6-hydroxydopamine were suppressed by perinatal morphine exposure whereas the association of morphine exposure and 6-hydroxydopamine lesion promoted the normal mRNA expression of the synaptic marker synapsin I.