背景:GABA,一种关键的抑制性神经递质,在突触后神经元上有突触和突触外受体。背景GABA,从突触间隙溢出,作用于含有GABAA受体的突触外δ亚基。突触外GABA能输入在偏头痛中的作用尚不清楚。我们研究了斯特拉斯堡大鼠遗传缺失癫痫(GAERS)对具有临床相关行为读数的有效偏头痛诱发物质的易感性,改变了GABA能张力。随后,我们通过药理学手段筛选了Wistar大鼠的相关GABA能机制,以确定其机制。
方法:Wistar和GAERS大鼠给药硝酸甘油(10mg/kg)或左克罗马卡林(1mg/kg)。使用vonFrey单丝和暗光盒评估机械异常性疼痛和畏光。GAT-1受体阻滞剂替加宾(5mg/kg)的作用,GABAB受体激动剂巴氯芬(2mg/kg),突触GABAA受体激动剂地西泮(1mg/kg),突触外GABAA受体激动剂加波沙朵(4mg/kg),和麝香酚(0.75mg/kg),对T型钙通道阻滞剂乙硫肟(100mg/kg)或突触GABAA受体拮抗剂氟马西尼(15mg/kg)对左克罗马卡林诱导的偏头痛表型进行筛选。
结果:与Wistar大鼠不同,注射硝酸甘油或左旋克罗卡林后,GAERS的机械性疼痛阈值或轻度厌恶没有降低。乙硫肟不能逆转GAERS的耐药表型,排除了T型钙通道功能障碍在这一现象中的作用。Tiagabine可预防Wistar大鼠左克罗马卡林引起的机械性异常性疼痛,表明在增强GABA溢出中起关键作用。巴氯芬不能缓解机械性异常性疼痛。地西泮未能减轻左旋克罗马卡林诱导的偏头痛表型。此外,GAERS的抗性表型不受氟马西尼的影响。突触外GABAA受体激动剂加波沙朵和麝香酚抑制Wistar大鼠眶周异常性疼痛。
结论:我们的研究引入了一种对偏头痛诱发剂具有抗性的大鼠品系,并表明突触外δGABA能受体的关键参与。突触外δGABAA受体,通过调节神经元兴奋性的恒定背景抑制,作为一种具有治疗潜力的新型药物靶标偏头痛。
BACKGROUND: GABA, a key inhibitory neurotransmitter, has synaptic and extrasynaptic receptors on the postsynaptic neuron. Background GABA, which spills over from the synaptic cleft, acts on extrasynaptic delta subunit containing GABAA receptors. The role of extrasynaptic GABAergic input in migraine is unknown. We investigated the susceptibility to valid migraine-provoking substances with clinically relevant behavioral readouts in Genetic Absence Epilepsy of Rats Strasbourg (GAERS), in which the GABAergic tonus was altered. Subsequently, we screened relevant GABAergic mechanisms in Wistar rats by pharmacological means to identify the mechanisms.
METHODS: Wistar and GAERS rats were administered nitroglycerin (10 mg/kg) or levcromakalim (1 mg/kg). Mechanical allodynia and photophobia were assessed using von Frey monofilaments and a dark-light box. Effects of GAT-1 blocker tiagabine (5 mg/kg), GABAB receptor agonist baclofen (2 mg/kg), synaptic GABAA receptor agonist diazepam (1 mg/kg), extrasynaptic GABAA receptor agonists gaboxadol (4 mg/kg), and muscimol (0.75 mg/kg), T-type calcium channel blocker ethosuximide (100 mg/kg) or synaptic GABAA receptor antagonist flumazenil (15 mg/kg) on levcromakalim-induced migraine phenotype were screened.
RESULTS: Unlike Wistar rats, GAERS exhibited no reduction in mechanical pain thresholds or light aversion following nitroglycerin or levcromakalim injection. Ethosuximide did not reverse the resistant phenotype in GAERS, excluding the role of T-type calcium channel dysfunction in this phenomenon. Tiagabine prevented levcromakalim-induced mechanical allodynia in Wistar rats, suggesting a key role in enhanced GABA spillover. Baclofen did not alleviate mechanical allodynia. Diazepam failed to mitigate levcromakalim-induced migraine phenotype. Additionally, the resistant phenotype in GAERS was not affected by flumazenil. Extrasynaptic GABAA receptor agonists gaboxadol and muscimol inhibited periorbital allodynia in Wistar rats.
CONCLUSIONS: Our study introduced a rat strain resistant to migraine-provoking agents and signified a critical involvement of extrasynaptic δGABAergic receptors. Extrasynaptic δ GABAA receptors, by mediating constant background inhibition on the excitability of neurons, stand as a novel drug target with a therapeutic potential in migraine.