Hippocampal long-term potentiation is reduced by chronic opiate treatment and can be restored by re-exposure to opiates.
Chronic exposure to opiates eventually leads to drug addiction, which is believed to involve maladaptive changes in brain function, but the underlying neuronal mechanisms remain primarily unknown. Given the known effects of opiates such as morphine and heroin on hippocampal function, we investigated the potential effect of chronic opiate treatment on long-term potentiation (LTP) at CA1 synapses in rat hippocampus, a leading experimental model for studying synaptic plasticity. Our results revealed that chronic exposure of rats to morphine or heroin, which induced severe drug tolerance and dependence, markedly reduced the capacity of hippocampal CA1 LTP during the period of drug withdrawal (from approximately 190% in control to approximately 120%). More interestingly, the capacity of LTP could be restored to the normal level by re-exposure of the animals to opiates, indicating that the synaptic function was already adapted to opiates. Morris water maze test, which measures behavioral consequences of synaptic plasticity, showed parallel learning deficits after chronic exposure to opiates. Moreover, the opiate-reduced LTP could also be restored by inhibitors of cAMP-dependent protein kinase A (PKA), suggesting that upregulation of cAMP pathway was likely one of the underlying mechanisms of the observed phenomena. These findings demonstrated that chronic opiate treatment can significantly modulate synaptic plasticity in the hippocampus, leading to an opiate dependence of the plasticity.
Pu
Lu
L
Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, People's Republic of China.
Bao
Guo-Bin
GB
Xu
Nan-Jie
NJ
Ma
Lan
L
Pei
Gang
G
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004334:Drug Administration Schedule; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D018756:GABA Antagonists / Q000494:pharmacology; D003932:Heroin / Q000008:administration & dosage; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D007279:Injections, Subcutaneous; D017774:Long-Term Potentiation / Q000187:drug effects* / Q000502:physiology; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D009020:Morphine / Q000008:administration & dosage; D009294:Narcotics / Q000494:pharmacology*; D009473:Neuronal Plasticity / Q000187:drug effects*; D009293:Opioid-Related Disorders / Q000503:physiopathology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D019966:Substance-Related Disorders; D013569:Synapses / Q000187:drug effects / Q000502:physiology
D004791:Enzyme Inhibitors; D018756:GABA Antagonists; D009294:Narcotics; D003932:Heroin; D009020:Morphine; D017868:Cyclic AMP-Dependent Protein Kinases