Naltrexone Facilitates Learning and Delays Extinction by Increasing AMPA Receptor Phosphorylation and Membrane Insertion

Abstract

Background The opioid antagonists, naloxone/naltrexone, are involved in improving learning and memory, but their cellular and molecular mechanisms remain unknown. We investigated the effect of naloxone/naltrexone on hippocampal AMPAR trafficking, a molecular substrate of learning and memory, as a probable mechanism for the antagonists activity. Methods To measure naloxone/naltrexone-regulated AMPAR trafficking, pHluorin-GluA1 imaging and biochemical analyses were performed on primary hippocampal neurons. To establish the in vivo role of GluA1-S845 phosphorylation on the behavioral effect induced by inhibition of the endogenous μ-opioid receptor (MOR) by naltrexone, MOR knockout (MORKO) and GluA1-S845A mutant (in which Ser845 was mutated to Ala) mice were tested in a water maze after chronic naltrexone administration. Behavioral responses and GluA1 levels in the hippocampal postsynaptic density (PSD) in wild-type and GluA1-S845A mutants mice were compared using Western blot analysis. Results In vitro prolonged naloxone/naltrexone exposure significantly increased synaptic and extrasynaptic GluA1 membrane expression as well as GluA1-S845 phosphorylation. In the MORKO and GluA1-S845A mutant mice, naltrexone did not improve learning, which suggests that naltrexone acts via inhibition of endogenous MOR action and alteration of GluA1 phosphorylation. Naltrexone-treated wild-type mice had significantly increased phosphorylated GluA1-S845 and GluA1 levels in their hippocampal PSD on the third day of acquisition, which is the time when naltrexone significantly improved learning. Conclusions The beneficial effect of naltrexone on spatial learning and memory under normal conditions appears to be the result of increasing GluA1-S845 phosphorylation-dependent AMPAR trafficking. These results can be further explored in a mouse model of memory loss.

M1 muscarinic receptor facilitates cognitive function by interplay with AMPA receptor GluAl subunit

“…To further investigate the role of GluA1 and its phosphorylation at Ser845 in M1 mAChR-mediated learning and memory, S485A mice were used in which phosphorylation of GluA1 at Ser845 was abrogated. Similar to a previous study showing that S845A mutant mice display normal hippocampus-dependent spatial reference memory in MWM with a larger 12-cm platform (34), performance of these mutant mice with a 4-cm platform was comparable to that of WT mice during the learning period and the probe test (S845A vehicle vs. WT vehicle) ( Fig. 6A, B, D, E).…”

“…Hippocampi were processed according to previous reports (34). The proteins were subjected to SDS-PAGE and immunoblotted with primary antibodies against M1 mAChR (1:1000; Frontier Institute, Hokkaido, Japan), GluA1 phosphorylated at Ser845 (1:1000; Abcam, Cambridge, United Kingdom), GluA1 phosphorylated at Ser831 (1:1000; Abcam), GluA1 (1:1000; Milli-poreSigma), PSD95 (1:1000; Santa Cruz Biotechnology), and GAPDH (1:1000; MilliporeSigma).…”

“…The Morris water maze (MWM) procedure was performed as previously described with mild modifications (34,35). The mice were trained in a 150-cm diameter circular pool filled with opaque water (30 cm deep, 19-22°C).…”

Changes in hippocampal AMPA receptors and cognitive impairments in chronic ketamine addiction models: another understanding of ketamine CNS toxicity

“…The method used to obtain post-synaptic membrane proteins from the mice hippocampi was a modification of previous procedures5051. Briefly, hippocampi from mice were gathered, resuspended in the solution of 0.32 mol/L sucrose, 4 mmol/L 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (pH 7.4) with protease/phosphatase inhibitors (Sigma-Aldrich, St. Louis, Missouri) and homogenized.…”

The Effect of Naltrexone on Memory Deficit Followed by Electroconvulsive Therapy: A Randomized, Double-Blind, Placebo-Controlled Trial

“…Lately, studies working on the impact of administration of opioid antagonists, such as naloxone and naltrexone, on memory expansion in lab animals have been performed (13,14). memory seems to be the result of augmenting GluA1-S845 phosphorylation-dependent AMPAR trafficking (16). Naltrexone and other toll like receptor 4 (TLR4) antagonists could cause an exquisite therapeutic method to reduce the main problems of memory or executive cognitive function disorder after cardiac arrest/cardiopulmonary resuscitation (14).…”