Conantokins Inhibit The Discovery And Preliminary Study Of The Mechanism Of Morphine Dependence In Mice

Conantokins are the important family of Conus peptides that target specific subtypes of N-Methyl-D-aspartate (NMD A) receptors and also the only one type of peptide inhibitors that have been discovered so far. NR2B subunit of NMDA receptor is involved in algesia, neurotoxicity and drug abuse. NR2B-selective inhibitor shows a great potential for the development of low side-effect drug for analgesia, neuroprotection and drug abstinence.Our previous experiemnts show that con-G and its variants exhibit potent inhibitory activity to the naloxone-induced withdrawal jumping in morphine dependent mice, and their inhibitory activity are dependent on the selectivity to NR2B subunit. However, the activity of conantokins and their variants on inhibiting morphine psychological dependence in mice has not been studied. Based on the previous results, we screened other conantokin variants and determined their activities and mechanism on inhibiting the development of morphine physical and psychological dependence. The results are as follows:(1) 21 Conantokins variants were screened, and a NR2B subunit-selective inhibitor con-T-[M8Q] with low side effects was found. Con-T-[M8Q] can not only effectively inhibit the expression and development of morphine physical dependence of mice, but also have not apparent side-effects on the motor function or locomotor activity in the dose used.(2) Con-T-[M8Q] can significantly attenuate the expression and development of the morphine psychological dependence. Con-T[M8Q] almost completely block morphine psychological dependence at the dose of 5nmol/kg.(3) The mechanism of the inhibitory effects of con-T-[M8Q] on morphine-dependent mice was studied and the results showed that con-T[M8Q] can inhibit the phosphorylation of Try 1472 of NR2B subunit of NMDA receptor in morphine-dependent mice and attenuate the expression of nonphosphorylation of NR2B subunit. The expression of CaMKⅡ,CaMKⅣmRNA of morphine-dependent mice decrease followed the increasing inhibitor except the expression of CaMKI mRNA. Con-T[M8Q] also can reduce the expression of ERK and c-fos.This study provided a good tool for studying the mechanism of morphine-dependence and reaction mechanism for the further application of NMDAR inhibitors.