Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, University of Calgary, Calgary AB T2N4N1, Canada
Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, 60126 Ancona, Italy.
J Neurosci. 2023 Jan 25;43(4):571-583. doi: 10.1523/JNEUROSCI.0541-22.2022. Epub 2022 Dec 2.
Repeated seizures result in a persistent maladaptation of endocannabinoid (eCB) signaling, mediated part by anandamide signaling deficiency in the basolateral amygdala (BLA) that manifests as aberrant synaptic function and altered emotional behavior. Here, we determined the effect of repeated seizures (kindling) on 2-arachidonoylglycerol (2-AG) signaling on GABA transmission by directly measuring tonic and phasic eCB-mediated retrograde signaling in an BLA slice preparation from male rats. We report that both activity-dependent and muscarinic acetylcholine receptor (mAChR)-mediated depression of GABA synaptic transmission was reduced following repeated seizure activity. These effects were recapitulated in sham rats by preincubating slices with the 2-AG synthesizing enzyme inhibitor DO34. Conversely, preincubating slices with the 2-AG degrading enzyme inhibitor KML29 rescued activity-dependent 2-AG signaling, but not mAChR-mediated synaptic depression, over GABA transmission in kindled rats. These effects were not attributable to a change in cannabinoid type 1 (CB1) receptor sensitivity or altered 2-AG tonic signaling since the application of the highly selective CB1 receptor agonist CP55,940 provoked a similar reduction in GABA synaptic activity in both sham and kindled rats, while no effect of either DO34 or of the CB1 inverse agonist AM251 was observed on frequency and amplitude of spontaneous IPSCs in either sham or kindled rats. Collectively, these data provide evidence that repeated amygdala seizures persistently alter phasic 2-AG-mediated retrograde signaling at BLA GABAergic synapses, probably by impairing stimulus-dependent 2-AG synthesis/release, which contributes to the enduring aberrant synaptic plasticity associated with seizure activity. The plastic reorganization of endocannabinoid (eCB) signaling after seizures and during epileptogenesis may contribute to the negative neurobiological consequences associated with seizure activity. Therefore, a deeper understanding of the molecular basis underlying the pathologic long-term eCB signaling remodeling following seizure activity will be crucial to the development of novel therapies for epilepsy that not only target seizure activity, but, most importantly, the epileptogenesis and the comorbid conditions associated with epilepsy.
反复的癫痫发作会导致内源性大麻素（eCB）信号持续适应不良，部分原因是外侧杏仁核（BLA）中的大麻素信号不足，表现为异常的突触功能和改变的情绪行为。在这里，我们通过直接测量雄性大鼠 BLA 切片中紧张性和相发性 eCB 介导的逆行信号，确定了反复癫痫发作（点燃）对 2-花生四烯酸甘油（2-AG）信号对 GABA 传递的影响。我们报告说，在反复的癫痫发作活动后，活性依赖性和毒蕈碱乙酰胆碱受体（mAChR）介导的 GABA 突触传递的抑制作用均减弱。这些作用可以通过在 Sham 大鼠的切片中预先孵育 2-AG 合成酶抑制剂 DO34 来重现。相反，预先孵育 2-AG 降解酶抑制剂 KML29 可挽救在点燃大鼠中 GABA 传递的活性依赖性 2-AG 信号，但不能挽救 mAChR 介导的突触抑制作用。这些作用不能归因于大麻素 1 型（CB1）受体敏感性的变化或改变的 2-AG 紧张性信号，因为高度选择性的 CB1 受体激动剂 CP55,940 在 Sham 和点燃大鼠中均引起 GABA 突触活性的相似降低，而 DO34 或 CB1 反向激动剂 AM251 对 Sham 或点燃大鼠中自发性 IPSC 的频率和幅度均无影响。总的来说，这些数据提供了证据，表明反复的杏仁核癫痫发作持续改变 BLA GABA 能突触的相发性 2-AG 介导的逆行信号，可能是通过损害刺激依赖性 2-AG 合成/释放，从而导致与癫痫发作活动相关的持久异常突触可塑性。癫痫发作后和癫痫发生期间内源性大麻素（eCB）信号的可塑性重排可能与与癫痫发作活动相关的负面神经生物学后果有关。因此，深入了解癫痫发作后病理性长期 eCB 信号重塑的分子基础对于开发针对癫痫的新型治疗方法至关重要，这些新型治疗方法不仅针对癫痫发作活动，而且最重要的是针对癫痫发生和与癫痫相关的合并症。
