Broadwater Margaret A, Liu Wen, Crews Fulton T, Spear Linda P
Bowles Center for Alcohol Studies, University of North Carolina at Chapel Hill, Chapel Hill, N.C., USA.
Dev Neurosci. 2014;36(3-4):297-305. doi: 10.1159/000362874. Epub 2014 Jun 27.
Although adolescence is a common age to initiate alcohol consumption, the long-term consequences of exposure to alcohol at this time of considerable brain maturation are largely unknown. In studies utilizing rodents, behavioral evidence is beginning to emerge suggesting that the hippocampus may be persistently affected by repeated ethanol exposure during adolescence, but not by comparable alcohol exposure in adulthood. The purpose of this series of experiments was to explore a potential mechanism of hippocampal dysfunction in adults exposed to ethanol during adolescence. Given that disruption in adult neurogenesis has been reported to impair performance on tasks thought to be hippocampally related, we used immunohistochemistry to assess levels of doublecortin (DCX), an endogenous marker of immature neurons, in the dentate gyrus (DG) of the hippocampus 3-4 weeks after adolescent (postnatal day, PD28-48) or adult (PD70-90) intermittent ethanol exposure to 4 g/kg ethanol administered intragastrically. We also investigated another neurogenic niche, the subventricular zone (SVZ), to determine if the effects of ethanol exposure were region specific. Levels of cell proliferation and cell death were also examined in the DG via assessing Ki67 and cleaved caspase-3 immunoreactivity, respectively. Significantly less DCX was observed in the DG of adolescent (but not adult) ethanol-exposed animals about 4 weeks after exposure when these animals were compared to control age-mates. The effects of adolescent ethanol on DCX immunoreactivity were specific to the hippocampus, with no significant exposure effects emerging in the SVZ. In both the DG and the SVZ there was a significant age-related decline in neurogenesis as indexed by DCX. The persistent effect of adolescent ethanol exposure on reduced DCX in the DG appears to be related to significant increases in cell death, with significantly more cleaved caspase-3-positive immunoreactivity observed in the adolescent ethanol group compared to controls, but no alterations in cell proliferation when indexed by Ki67. These results suggest that a history of adolescent ethanol exposure results in lowered levels of differentiating neurons, probably due at least in part to increased cell death of immature neurons. These effects were evident in adulthood, weeks following termination of the chronic exposure, and may contribute to previously reported behavioral deficits on hippocampal-related tasks after chronic ethanol exposure in adolescence.
尽管青春期是开始饮酒的常见年龄，但在大脑显著成熟的这个时期接触酒精的长期后果在很大程度上尚不清楚。在利用啮齿动物进行的研究中，行为学证据开始出现，表明海马体可能会受到青春期反复乙醇暴露的持续影响，但成年期同等程度的酒精暴露则不会产生这种影响。这一系列实验的目的是探究青春期接触乙醇的成年个体海马体功能障碍的潜在机制。鉴于据报道成年神经发生的破坏会损害被认为与海马体相关的任务表现，我们使用免疫组织化学方法评估了在青春期（出生后第28 - 48天）或成年期（出生后第70 - 90天）间歇性经胃给予4 g/kg乙醇后3 - 4周，海马齿状回（DG）中未成熟神经元的内源性标志物双皮质素（DCX）的水平。我们还研究了另一个神经发生微环境，即脑室下区（SVZ），以确定乙醇暴露的影响是否具有区域特异性。通过分别评估Ki67和裂解的半胱天冬酶 - 3免疫反应性，还在DG中检测了细胞增殖和细胞死亡水平。与同龄对照动物相比，在暴露后约4周时，青春期（而非成年期）乙醇暴露动物的DG中观察到的DCX显著减少。青春期乙醇对DCX免疫反应性的影响仅限于海马体，在SVZ中未出现显著的暴露效应。在DG和SVZ中，以DCX为指标的神经发生均出现了与年龄相关的显著下降。青春期乙醇暴露对DG中DCX减少的持续影响似乎与细胞死亡的显著增加有关，与对照组相比，青春期乙醇组中观察到的裂解的半胱天冬酶 - 3阳性免疫反应性显著更多，但以Ki67为指标时细胞增殖没有变化。这些结果表明，青春期乙醇暴露史导致分化神经元水平降低，这可能至少部分归因于未成熟神经元细胞死亡的增加。这些影响在成年期、慢性暴露终止数周后仍然明显，并且可能导致先前报道的青春期慢性乙醇暴露后与海马体相关任务的行为缺陷。
