Liu Dongyu, Fujihara Kazuyuki, Yanagawa Yuchio, Mushiake Hajime, Ohshiro Tomokazu
Department of Physiology, Graduate School of Medicine, Tohoku University, Sendai, Japan.
Department of Psychiatry and Neuroscience, Graduate School of Medicine, Gunma University, Maebashi, Japan.
Front Neurol. 2023 Sep 26;14:1243301. doi: 10.3389/fneur.2023.1243301. eCollection 2023.
To elucidate the functional role of gamma-aminobutyric acid (GABA)-ergic inhibition in suppressing epileptic brain activities such as spike-wave discharge (SWD), we recorded electroencephalogram (EEG) in knockout rats for (), which encodes one of the two GABA-synthesizing enzymes in mammals. We also examined how anti-epileptic drug valproate (VPA) acts on the SWDs present in rats and affects GABA synthesis in the reticular thalamic nucleus (RTN), which is known to play an essential role in suppressing SWD.
Chronic EEG recordings were performed in freely moving control rats and homozygous knockout (-/-) rats. Buzzer tones (82 dB) were delivered to the rats during EEG monitoring to test whether acoustic stimulation could interrupt ongoing SWDs. VPA was administered orally to the rats, and the change in the number of SWDs was examined. The distribution of GABA in the RTN was examined immunohistochemically.
SWDs were abundant in EEG from (-/-) rats as young as 2 months old. Although SWDs were universally detected in older rats irrespective of their genotype, SWD symptom was most severe in (-/-) rats. Acoustic stimulation readily interrupted ongoing SWDs irrespective of the genotype, whereas SWDs were more resistant to interruption in (-/-) rats. VPA treatment alleviated SWD symptoms in control rats, however, counterintuitively exacerbated the symptoms in (-/-) rats. The immunohistochemistry results indicated that GABA immunoreactivity was significantly reduced in the somata of RTN neurons in (-/-) rats but not in their axons targeting the thalamus. VPA treatment greatly increased GABA immunoreactivity in the RTN neurons of (-/-) rats, which is likely due to the intact GAD2, another GAD isozyme, in these neurons.
Our results revealed two opposing roles of GABA in SWD generation: suppression and enhancement of SWD. To account for these contradictory roles, we propose a model in which GABA produced by GAD1 in the RTN neuronal somata is released extrasynaptically and mediates intra-RTN inhibition.
为阐明γ-氨基丁酸（GABA）能抑制在抑制癫痫性脑活动（如棘波放电（SWD））中的功能作用，我们在敲除大鼠中记录脑电图（EEG），该基因编码哺乳动物中两种GABA合成酶之一。我们还研究了抗癫痫药物丙戊酸（VPA）如何作用于大鼠中存在的SWD，并影响丘脑网状核（RTN）中的GABA合成，已知该核在抑制SWD中起重要作用。
在自由活动的对照大鼠和纯合敲除（-/-）大鼠中进行慢性EEG记录。在EEG监测期间向大鼠发出蜂鸣音（82分贝），以测试声刺激是否能中断正在进行的SWD。给大鼠口服VPA，并检查SWD数量的变化。通过免疫组织化学检查RTN中GABA的分布。
在2个月大的（-/-）大鼠的EEG中，SWD很丰富。尽管在老年大鼠中普遍检测到SWD，而与它们的基因型无关，但SWD症状在（-/-）大鼠中最为严重。无论基因型如何，声刺激都能轻易中断正在进行的SWD，而在（-/-）大鼠中，SWD对中断更具抗性。VPA治疗减轻了对照大鼠的SWD症状，然而，与直觉相反的是，在（-/-）大鼠中加剧了症状。免疫组织化学结果表明，（-/-）大鼠RTN神经元胞体中的GABA免疫反应性显著降低，但在其靶向丘脑的轴突中没有降低。VPA治疗大大增加了（-/-）大鼠RTN神经元中的GABA免疫反应性，这可能是由于这些神经元中完整的另一种GAD同工酶GAD2。
我们的结果揭示了GABA在SWD产生中的两种相反作用：抑制和增强SWD。为了解释这些矛盾的作用，我们提出了一个模型，其中RTN神经元胞体中由GAD1产生的GABA通过突触外释放并介导RTN内抑制。
