Department of Psychiatry, Institute of Psychiatric Research, Indiana University School of Medicine, Indianapolis, Indiana.
Department of Psychiatry, University of Illinois at Chicago, Chicago, Illinois.
Alcohol Clin Exp Res. 2017 Nov;41(11):1896-1906. doi: 10.1111/acer.13488. Epub 2017 Oct 3.
A Grm2 cys407* stop codon mutation, which results in a loss of the metabotropic glutamate 2 (mGlu2) receptor protein, was identified as being associated with high alcohol drinking by alcohol-preferring (P) rats. The objectives of the current study were to characterize the effects of reduced levels of mGlu2 receptors on glutamate transmission and alcohol drinking.
Quantitative no-net-flux microdialysis was used to test the hypothesis that basal extracellular glutamate levels in the prelimbic (PL) cortex and nucleus accumbens shell (NACsh) will be higher in P than Wistar rats. A lentiviral-delivered short-hairpin RNA (shRNA)-mediated knockdown was used to test the hypothesis that reduced levels of mGlu2 receptors within the PL cortex will increase voluntary alcohol drinking by Wistar rats. A linear regression analysis was used to test the hypothesis that there will be a significant correlation between the Grm2 cys407* mutation and level of alcohol intake.
Extracellular glutamate concentrations within the PL cortex (3.6 ± 0.6 vs. 6.4 ± 0.6 μM) and NACsh (3.2 ± 0.4 vs. 6.6 ± 0.6 μM) were significantly lower in female P than female Wistar rats. Western blot detected the presence of mGlu2 receptors in these regions of female Wistar rats, but not female P rats. Micro-infusion of shRNAs into the PL cortex significantly reduced local mGlu2 receptor levels (by 40%), but did not alter voluntary alcohol drinking in male Wistar rats. In addition, there was no significant correlation between the Grm2 mutation and alcohol intake in 36 rodent lines (r = 0.29, p > 0.05).
Collectively, these results suggest a lack of association between the loss of mGlu2 receptors and glutamate transmission in the NACsh and PL cortex of female P rats, and between the level of mGlu2 receptors in the PL cortex and alcohol drinking of male Wistar rats.
甘氨酸 2 型谷氨酸受体（mGlu2）的一个 Cys407* 点突变导致该受体蛋白缺失，这与酒精偏好（P）大鼠的高饮酒量有关。本研究的目的是探讨 mGlu2 受体水平降低对谷氨酸传递和酒精摄入的影响。
使用无净流量微量透析法检测 Prefrontal 皮质（PL）和伏隔核壳（NACsh）细胞外谷氨酸基础水平，以验证 P 大鼠比 Wistar 大鼠的 PL 皮质和 NACsh 细胞外谷氨酸基础水平更高的假设。利用慢病毒传递短发夹 RNA（shRNA）介导的敲低技术，检测 PL 皮质 mGlu2 受体水平降低是否会增加 Wistar 大鼠的自愿性饮酒量。线性回归分析用于检测 Grm2 基因 Cys407* 突变与饮酒量之间是否存在显著相关性。
与 Wistar 大鼠相比，雌性 P 大鼠 PL 皮质（3.6±0.6 vs. 6.4±0.6 μM）和 NACsh（3.2±0.4 vs. 6.6±0.6 μM）细胞外谷氨酸浓度显著降低。Western blot 检测到 Wistar 大鼠 PL 皮质存在 mGlu2 受体，但 P 大鼠没有。将 shRNA 微注射到 PL 皮质可显著降低局部 mGlu2 受体水平（降低 40%），但不会改变雄性 Wistar 大鼠的自愿性饮酒量。此外，在 36 条啮齿动物品系中，Grm2 突变与饮酒量之间无显著相关性（r=0.29，p>0.05）。
综上所述，本研究结果提示，雌性 P 大鼠 NACsh 和 PL 皮质 mGlu2 受体缺失与谷氨酸传递之间，以及雄性 Wistar 大鼠 PL 皮质 mGlu2 受体水平与酒精摄入之间，均不存在相关性。
