Gordey M, Mekmanee L, Mody I
Department of Neurology, UCLA School of Medicine, Los Angeles, CA 90095, USA.
Neuroscience. 2001;105(4):987-97. doi: 10.1016/s0306-4522(01)00234-2.
Phosphorylation of C-termini of receptor subunits is thought to play a significant role in modulation of N-methyl-D-aspartic acid (NMDA) receptor function. To investigate whether the C-terminus of the NR2A subunit is involved in determining the sensitivity of NMDA receptors to ethanol we compared the effects of ethanol in vitro on NMDA-mediated field excitatory postsynaptic potentials (fEPSPs) in the CA1 and dentate gyrus (DG) of adult male NR2A(DeltaC/DeltaC) mice lacking the C-terminus of NR2A subunit and in their parental strain C57Bl/6. We also tested the in vivo effects of a hypnotic dose of ethanol in C57Bl/6 and NR2A(DeltaC/DeltaC) mice and their F2 offspring. Ifenprodil (10 microM) was used to distinguish between the NR2A and NR2B components of NMDA fEPSPs. Ethanol (100 mM) in the presence of ifenprodil inhibited the CA1 NR2A-mediated component of NMDA fEPSPs two times more in NR2A(DeltaC/DeltaC) than in C57Bl/6. Ethanol inhibition of the CA1 NR2B-mediated component was five to seven times lower in NR2A(DeltaC/DeltaC) than in C57Bl/6. In the DG ethanol had similar effects in the two strains. In vivo administration of ethanol (4 g/kg) induced sedation of similar duration in both strains of mice. A second administration of ethanol 7 days after the initial injection revealed an increased ethanol sensitivity of NR2A(DeltaC/DeltaC) and F2(DeltaC/DeltaC) mice including a shortened time to loss of righting reflex and an increased sleep time. The sensitization of NR2A(DeltaC/DeltaC) mice to alcohol was not accompanied by an altered ethanol sensitivity of NMDA fEPSPs recorded in vitro. Our data are consistent with the inhibitory action of ethanol on NMDA receptors being mediated by a site other than the intracellular C-terminus of the NR2A subunit. The altered sensitivities to ethanol of both NR2A- and NR2B-mediated responses in the CA1 of NR2A(DeltaC/DeltaC) imply that NR2A- and NR2B subunit-containing NMDA receptors may be linked by a common target of ethanol.
受体亚基C末端的磷酸化被认为在N-甲基-D-天冬氨酸（NMDA）受体功能调节中起重要作用。为了研究NR2A亚基的C末端是否参与决定NMDA受体对乙醇的敏感性，我们比较了乙醇体外对成年雄性NR2A(DeltaC/DeltaC)小鼠（缺乏NR2A亚基的C末端）及其亲本品系C57Bl/6的CA1和齿状回（DG）中NMDA介导的场兴奋性突触后电位（fEPSP）的影响。我们还测试了催眠剂量的乙醇对C57Bl/6和NR2A(DeltaC/DeltaC)小鼠及其F2后代的体内作用。使用ifenprodil（10 microM）区分NMDA fEPSP的NR2A和NR2B成分。在ifenprodil存在下，乙醇（100 mM）对NR2A(DeltaC/DeltaC)小鼠CA1中NMDA fEPSP的NR2A介导成分的抑制作用比对C57Bl/6小鼠的抑制作用强两倍。乙醇对NR2A(DeltaC/DeltaC)小鼠CA1中NR2B介导成分的抑制作用比对C57Bl/6小鼠的抑制作用低五到七倍。在DG中，乙醇对两种品系小鼠的作用相似。体内给予乙醇（4 g/kg）在两种品系小鼠中诱导的镇静持续时间相似。首次注射后7天再次给予乙醇显示，NR2A(DeltaC/DeltaC)和F2(DeltaC/DeltaC)小鼠对乙醇的敏感性增加，包括翻正反射消失时间缩短和睡眠时间增加。NR2A(DeltaC/DeltaC)小鼠对酒精的敏感性增加并未伴随体外记录的NMDA fEPSP对乙醇敏感性的改变。我们的数据与乙醇对NMDA受体的抑制作用由NR2A亚基细胞内C末端以外的位点介导一致。NR2A(DeltaC/DeltaC)小鼠CA1中NR2A和NR2B介导反应对乙醇敏感性的改变意味着含NR2A和NR2B亚基的NMDA受体可能通过乙醇的共同靶点相连。
