Karacay Bahri, Mahoney Jo, Plume Jeffrey, Bonthius Daniel J
Department of Pediatrics , University of Iowa College of Medicine, Iowa City, Iowa.
Alcohol Clin Exp Res. 2015 Feb;39(2):221-31. doi: 10.1111/acer.12615. Epub 2015 Feb 9.
Prenatal alcohol exposure can kill developing neurons, leading to microencephaly and mental retardation. However, not all fetuses are equally vulnerable to alcohol's neurotoxic effects. While some fetuses are severely affected and are ultimately diagnosed with fetal alcohol syndrome (FAS), others have no evidence of neuropathology and are behaviorally normal. These widely different outcomes among alcohol-exposed fetuses are likely due, in part, to genetic differences. Some fetuses possess genotypes that make them much more vulnerable than others to alcohol's teratogenic effects. However, to date, only 1 gene has been identified whose mutation can worsen alcohol-induced behavioral deficits in an animal model of FAS. That gene is neuronal nitric oxide synthase (nNOS). The purpose of this study was to determine whether mutation of nNOS can likewise worsen alcohol-induced microencephaly and lead to permanent neuronal deficits.
Wild-type and nNOS(-/-) mice received alcohol (0.0, 2.2, or 4.4 mg/g) daily over postnatal days (PDs) 4 to 9. Beginning on PD 85, the mice underwent a series of behavioral tests; the results of which are reported in the companion paper. The brains were then weighed, and stereological cell counts were performed on the cerebral cortex and hippocampal formation, which are the brain regions that mediate the aforementioned behavioral tasks.
Alcohol caused dose-dependent microencephaly, but only in the nNOS(-/-) mice and not in wild-type mice. Alcohol-induced neuronal losses were more severe in the nNOS(-/-) mice than in the wild-type mice in all of the brain regions examined, including the cerebral cortex, hippocampal CA3 subregion, hippocampal CA1 subregion, and dentate gyrus.
Targeted mutation of the nNOS gene increases the vulnerability of the developing brain to alcohol-induced growth restriction and neuronal losses. This increased neuropathology is associated with worsened behavioral dysfunction. The results demonstrate the critical importance of genotype in determining the outcome of developmental alcohol exposure.
孕期酒精暴露可导致发育中的神经元死亡，进而引发小头畸形和智力发育迟缓。然而，并非所有胎儿对酒精的神经毒性作用都同样敏感。虽然一些胎儿受到严重影响并最终被诊断为胎儿酒精综合征（FAS），但其他胎儿并无神经病理学证据且行为正常。酒精暴露胎儿中这些差异极大的结果可能部分归因于基因差异。一些胎儿所具有的基因型使他们比其他胎儿更容易受到酒精致畸作用的影响。然而，迄今为止，仅发现1个基因，其突变会使FAS动物模型中酒精诱导的行为缺陷恶化。该基因是神经元型一氧化氮合酶（nNOS）。本研究的目的是确定nNOS突变是否同样会使酒精诱导的小头畸形恶化并导致永久性神经元缺陷。
野生型和nNOS基因敲除（nNOS(-/-)）小鼠在出生后第4至9天每天接受酒精（0.0、2.2或4.4毫克/克）。从出生后第85天开始，对小鼠进行一系列行为测试；其结果在配套论文中报道。然后称量大脑重量，并对大脑皮层和海马结构进行立体细胞计数，这两个脑区介导上述行为任务。
酒精导致剂量依赖性小头畸形，但仅在nNOS(-/-)小鼠中出现，野生型小鼠未出现。在所有检测的脑区，包括大脑皮层、海马CA3亚区、海马CA1亚区和齿状回，酒精诱导的神经元损失在nNOS(-/-)小鼠中比野生型小鼠更严重。
nNOS基因的靶向突变增加了发育中大脑对酒精诱导的生长受限和神经元损失的易感性。这种神经病理学加重与行为功能障碍恶化相关。结果表明基因型在决定发育性酒精暴露结局方面至关重要。
