Premium
Opioid withdrawal for 4 days prevents synaptic depression induced by low dose of morphine or naloxone in rat hippocampal CA1 area in vivo
Author(s) -
Dong Zhifang,
Han Huili,
Cao Jun,
Xu Lin
Publication year - 2010
Publication title -
hippocampus
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.767
H-Index - 155
eISSN - 1098-1063
pISSN - 1050-9631
DOI - 10.1002/hipo.20638
Subject(s) - long term potentiation , (+) naloxone , opioid , hippocampal formation , synaptic plasticity , morphine , antagonist , opioid receptor , pharmacology , chemistry , neuroscience , anesthesia , medicine , psychology , receptor
Abstract 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. © 2009 Wiley‐Liss, Inc.