Reddy Sandesh D, Younus Iyan, Clossen Bryan L, Reddy Doodipala Samba
Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas.
Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas
J Pharmacol Exp Ther. 2015 Jun;353(3):517-28. doi: 10.1124/jpet.114.222075. Epub 2015 Mar 17.
Midazolam is a benzodiazepine anticonvulsant with rapid onset and short duration of action. Midazolam is the current drug of choice for acute seizures and status epilepticus, including those caused by organophosphate nerve agents. The antiseizure activity of midazolam is thought to result from its allosteric potentiation of synaptic GABA(A) receptors in the brain. However, there are indications that benzodiazepines promote neurosteroid synthesis via the 18-kDa cholesterol transporter protein (TSPO). Therefore, we investigated the role of neurosteroids and their extrasynaptic GABA(A) receptor targets in the antiseizure activity of midazolam. Here, we used δ-subunit knockout (DKO) mice bearing a targeted deletion of the extrasynaptic receptors to investigate the contribution of the extrasynaptic receptors to the antiseizure activity of midazolam using the 6-Hz and hippocampus kindling seizure models. In both models, midazolam produced rapid and dose-dependent protection against seizures (ED50, 0.4 mg/kg). Moreover, the antiseizure potency of midazolam was undiminished in DKO mice compared with control mice. Pretreatment with PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide], a TSPO blocker, or finasteride, a 5α-reductase neurosteroid inhibitor, did not affect the antiseizure effect of midazolam. The antiseizure activity of midazolam was significantly reversed by pretreatment with flumazenil, a benzodiazepine antagonist. Plasma and brain levels of the neurosteroid allopregnanolone were not significantly greater in midazolam-treated animals. These studies therefore provide strong evidence that neurosteroids and extrasynaptic GABA(A) receptors are not involved in the antiseizure activity of midazolam, which mainly occurs through synaptic GABA(A) receptors via direct binding to benzodiazepine sites. This study reaffirms midazolam's use for controlling acute seizures and status epilepticus.
咪达唑仑是一种苯二氮䓬类抗惊厥药，起效迅速，作用时间短。咪达唑仑是目前治疗急性惊厥和癫痫持续状态的首选药物，包括由有机磷酸酯类神经毒剂引起的惊厥和癫痫持续状态。咪达唑仑的抗惊厥活性被认为是由于其对大脑中突触GABA(A)受体的变构增强作用。然而，有迹象表明苯二氮䓬类药物通过18 kDa胆固醇转运蛋白（TSPO）促进神经甾体的合成。因此，我们研究了神经甾体及其突触外GABA(A)受体靶点在咪达唑仑抗惊厥活性中的作用。在此，我们使用携带突触外受体靶向缺失的δ亚基敲除（DKO）小鼠，通过6 Hz和海马点燃癫痫模型研究突触外受体对咪达唑仑抗惊厥活性的贡献。在这两种模型中，咪达唑仑均能迅速产生剂量依赖性的抗惊厥作用（半数有效剂量，0.4 mg/kg）。此外，与对照小鼠相比，咪达唑仑在DKO小鼠中的抗惊厥效力并未降低。用TSPO阻滞剂PK11195 [1-(2-氯苯基)-N-甲基-N-(1-甲基丙基)-3-异喹啉甲酰胺]或5α-还原酶神经甾体抑制剂非那雄胺预处理，并不影响咪达唑仑的抗惊厥作用。用苯二氮䓬类拮抗剂氟马西尼预处理可显著逆转咪达唑仑的抗惊厥活性。在咪达唑仑治疗的动物中，神经甾体别孕烯醇酮的血浆和脑水平并无显著升高。因此，这些研究提供了有力证据，表明神经甾体和突触外GABA(A)受体不参与咪达唑仑的抗惊厥活性，其抗惊厥活性主要通过与苯二氮䓬位点直接结合，经由突触GABA(A)受体发挥作用。本研究再次肯定了咪达唑仑在控制急性惊厥和癫痫持续状态方面的应用。
