Chronic morphine treatment modulates the extracellular levels of endogenous enkephalins in rat brain structures involved in opiate dependence: a microdialysis study.

摘要: The endogenous opioid system is often assumed to play a role in vulnerability drug abuse. However, controversial results have been reported regarding the levels of enkephalins or preproenkephalin neurons rodent brains after opiate administration. present study was performed determine extracellular and its physiological antagonist cholecystokinin (CCK), using vivo microdialysis freely moving rats morphine-induced physical dependence positive place conditioning. A large increase (340%) Met-enkephalin observed periaqueductal gray matter, structure involved morphine withdrawal syndrome, morphine-dependent rats. No change CCK immunoreactivity occurred these conditions. Moreover, conditioning preference paradigm, we for first time opposite changes enkephalin outflow nucleus accumbens (NAc). Thus, an placed drug-associated compartment decrease saline-paired side. These peptides NAc may reflect "emotional state" animals relation expectation reward (reinforcing effects morphine). lack regulation suggests that CCK-opioid interactions involve probably post-receptor events.