Programming for increased expression of hippocampal GAD67 mediated the hypersensitivity of the hypothalamic-pituitary-adrenal axis in male offspring rats with prenatal ethanol exposure.

An imbalance of excitatory and inhibitory signals in the brain has been proposed to be one of the main pathological features of various diseases related to hypothalamic–pituitary–adrenal axis (HPAA) dysfunction. Excessive glutamate release induces neuronal excitotoxicity, while glutamic acid decarboxylase (GAD) 67 promotes the transformation of excessive glutamate to γ-aminobutyric acid (GABA). Our previous studies demonstrated that prenatal ethanol exposure (PEE) causes foetal over-exposure to maternal corticosterone and hypersensitivity of the HPAA after birth, but its intrauterine programming mechanism is unknown. In this study, PEE was shown to lead to an enhanced potential excitatory ability of the hypothalamus and hypersensitivity of the HPAA, as well as mild abnormal hippocampal morphology, demethylation of the -1019 to -691-bp region in the hippocampal GAD67 promoter and upregulation of GAD67 expression accompanied by a reduction in glutamatergic neurons and increase in GABAergic neurons in PEE male offspring. Similar changes were also found in PEE male foetal rats. Furthermore, corticosterone increased the expression of the glucocorticoid receptor (GR) and GAD67 in foetal hippocampal H19-7 cells in a concentration-dependent manner, accompanied by demethylation of the GAD67 promoter, a decrease in glutamatergic neurons and increase in GABAergic neurons. The GR inhibitor, mifepristone, reversed the effects of corticosterone on H19-7 cells. These results suggested that PEE-induced excessive corticosterone can lead to upregulation of GAD67 through epigenetic modification mediated by the GR in the male foetal hippocampus, thereby weakening the negative regulation of the HPAA by the hippocampus and increasing the potential excitatory ability of the hypothalamus. These changes persisted until after birth, resulting in hypersensitivity of the HPAA. However, gender differences were observed in the hippocampal development, morphology and GAD67 expression associated with PEE. Programming for the increased expression of hippocampal GAD67 is a potential mechanism responsible for the hypersensitivity of the HPAA in PEE male rats.

大脑中兴奋性和抑制性信号的失衡被认为是与下丘脑 - 垂体 - 肾上腺轴（HPAA）功能障碍相关的多种疾病的主要病理特征之一。过量的谷氨酸释放会诱导神经元兴奋性毒性，而谷氨酸脱羧酶（GAD）67促进过量谷氨酸向γ - 氨基丁酸（GABA）的转化。我们先前的研究表明，产前乙醇暴露（PEE）会导致胎儿过度暴露于母体皮质酮，并在出生后出现HPAA超敏反应，但其宫内编程机制尚不清楚。在本研究中，发现PEE会导致下丘脑潜在兴奋性增强和HPAA超敏，以及海马形态轻度异常，海马GAD67启动子的 - 1019至 - 691bp区域去甲基化，GAD67表达上调，同时伴有PEE雄性子代谷氨酸能神经元减少和γ - 氨基丁酸能神经元增加。在PEE雄性胎鼠中也发现了类似的变化。此外，皮质酮以浓度依赖的方式增加胎鼠海马H19 - 7细胞中糖皮质激素受体（GR）和GAD67的表达，同时伴有GAD67启动子去甲基化、谷氨酸能神经元减少和γ - 氨基丁酸能神经元增加。GR抑制剂米非司酮逆转了皮质酮对H19 - 7细胞的作用。这些结果表明，PEE诱导的皮质酮过量可通过雄性胎鼠海马中GR介导的表观遗传修饰导致GAD67上调，从而削弱海马对HPAA的负性调节并增加下丘脑的潜在兴奋性。这些变化持续到出生后，导致HPAA超敏。然而，在与PEE相关的海马发育、形态和GAD67表达方面观察到了性别差异。海马GAD67表达增加的编程是导致PEE雄性大鼠HPAA超敏的一种潜在机制。