Opioid withdrawal for 4 days prevents synaptic depression induced by low dose of morphine or naloxone in rat hippocampal CA1 area in vivo.
The formation of memory is believed to depend on experience- or activity-dependent synaptic plasticity, which is exquisitely sensitive to psychological stress since inescapable stress impairs long-term potentiation (LTP) but facilitates long-term depression (LTD). Our recent studies demonstrated that 4 days of opioid withdrawal enables maximal extents of both hippocampal LTP and drug-reinforced behavior; while elevated-platform stress enables these phenomena at 18 h of opioid withdrawal. Here, we examined the effects of low dose of morphine (0.5 mg kg(-1), i.p.) or the opioid receptor antagonist naloxone (1 mg kg(-1), i.p.) on synaptic efficacy in the hippocampal CA1 region of anesthetized rats. A form of synaptic depression was induced by low dose of morphine or naloxone in rats after 18 h but not 4 days of opioid withdrawal. This synaptic depression was dependent on both N-methyl-D-aspartate receptor and synaptic activity, similar to the hippocampal long-term depression induced by low frequency stimulation. Elevated-platform stress given 2 h before experiment prevented the synaptic depression at 18 h of opioid withdrawal; in contrast, the glucocorticoid receptor (GR) antagonist RU38486 treatment (20 mg kg(-1), s.c., twice per day for first 3 days of withdrawal), or a high dose of morphine reexposure (15 mg kg(-1), s.c., 12 h before experiment), enabled the synaptic depression on 4 days of opioid withdrawal. This temporal shift of synaptic depression by stress or GR blockade supplements our previous findings of potentially correlated temporal shifts of LTP induction and drug-reinforced behavior during opioid withdrawal. Our results therefore support the idea that stress experience during opioid withdrawal may modify hippocampal synaptic plasticity and play important roles in drug-associated memory. (c) 2009 Wiley-Liss, Inc.
Key Laboratory of Animal Models and Human Disease Mechanisms, Kunming, People's Republic of China.
Zhifang
Z
Dong
Huili
H
Han
Jun
J
Cao
Lin
L
Xu
D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D056547:CA1 Region, Hippocampal / Q000187:drug effects* / Q000502:physiology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D008297:Male; D015735:Mifepristone / Q000008:administration & dosage / Q000494:pharmacology; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D009473:Neuronal Plasticity / Q000187:drug effects*; D009293:Opioid-Related Disorders / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011965:Receptors, Glucocorticoid / Q000037:antagonists & inhibitors; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D013315:Stress, Psychological / Q000503:physiopathology; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D011965:Receptors, Glucocorticoid; D016194:Receptors, N-Methyl-D-Aspartate; D015735:Mifepristone; D009270:Naloxone; D009020:Morphine