Morphine treatment increases clonidine binding in brain cell cultures

Exposure of murine brain cells in culture to 75 μM morphine for 6 days produced an increase in the number of [³H]clonidine binding sites without affecting the apparent affinity. Similar treatment increased the binding of this α₂-adrenergic receptor agonist to cell cultures prepared from cerebral cortex but not to cultures of brain minus cortex or to neuroblastoma-glioma hybrid cells which possess both opiate and α₂-adrenergic receptors.