Perinatal morphine II: changes in cortical plasticity.

We have previously shown that perinatal exposure to morphine impairs reactive plasticity of serotonin (5-HT) neurons following selective neonatal lesion (Gorio et al., J Neurosci Res 34:462-471, 1993). This study shows that morphine inhibits also that the compensatory sprouting of intact axons after partial denervation. Neonatal 6-OHDA injection causes norepinephrine (NE) depletion in the frontal cortex, which triggers a compensatory increase of dopamine, serotonin (5-HT), and met-enkephalin content correlated by the increased density of tyrosine hydroxylase- and 5-HT-positive axons. In perinatal morphine-treated rats, no compensatory changes are observed after neonatal 6-OHDA depletion of NE in the frontal cortex.