Department of Anesthesia, Critical Care and Pain Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA.
Department of Anesthesia, Harvard Medical School, Boston, MA, USA.
Cephalalgia. 2024 Sep;44(9):3331024241278919. doi: 10.1177/03331024241278919.
OnabotulinumtoxinA (onabotA), is assumed to achieve its therapeutic effect in migraine through blocking activation of unmyelinated meningeal nociceptors and their downstream communications with central dura-sensitive trigeminovascular neurons in the spinal trigeminal nucleus (SPV). The present study investigated the mechanism of action of onabotA by assessing its effect on activation and sensitization of dura-sensitive neurons in the SPV by cortical spreading depression (CSD). It is a follow up to our recent study on onabotA effects on activation and sensitization of peripheral trigeminovascular neurons.
In anesthetized male and female rats, single-unit recordings were used to assess effects of extracranial injections of onabotA (five injections, one unit each, diluted in 5 μl of saline were made along the lambdoid (two injection sites) and sagittal (two injection sites) suture) vs. vehicle on CSD-induced activation and sensitization of high-threshold (HT) and wide-dynamic range (WDR) dura-sensitive neurons in the SPV.
Single cell analysis of onabotA pretreatment effects on CSD-induced activation and sensitization of central trigeminovascular neurons in the SPV revealed the ability of this neurotoxin to prevent activation and sensitization of WDR neurons (13/20 (65%) vs. 4/16 (25%) activated neurons in the control vs. treated groups, = 0.022, Fisher's exact). By contrast, onabotA pretreatment effects on CSD-induced activation and sensitization of HT neurons had no effect on their activation (12/18 (67%) vs. 4/7 (36%) activated neurons in the control vs. treated groups, = 0.14, Fisher's exact). Regarding sensitization, we found that onabotA pretreatment prevented the enhanced responses to mechanical stimulation of the skin (i.e. responses reflecting central sensitization) in both WDR and HT neurons. In control but not treated WDR neurons, responses to brush (0.004 vs. 0.007), pressure (= 0.002 vs. = 0.79) and pinch (= 0.007 vs. 0.79) increased significantly two hours after CSD. Similarly, in control but not treated HT neurons, responses to brush (0.002 vs. 0.79), pressure (= 0.002 vs. = 0.72) and pinch (= 0.0006 vs. = 0.28) increased significantly two hours after CSD. Unexpectedly, onabotA pretreatment prevented the enhanced responses of both WDR and HT neurons to mechanical stimulation of the dura (commonly reflecting peripheral sensitization). In control vs. treated WDR and HT neurons, responses to dural stimulation were enhanced in 70 vs. 25% ( = 0.017) and 78 vs. 27% ( = 0.017), respectively.
The ability of onabotA to prevent activation and sensitization of WDR neurons is attributed to its preferential inhibitory effects on unmyelinated C-fibers. The inability of onabotA to prevent activation of HT neurons is attributed to its less extensive inhibitory effects on the thinly myelinated Aδ-fibers. These findings provide further pre-clinical evidence about differences and potentially complementary mechanisms of action of onabotA and calcitonin gene-related peptide-signaling neutralizing drugs.
肉毒杆菌毒素 A（onabotA）被认为通过阻断无髓脑膜伤害感受器的激活及其在脊髓三叉神经核（SPV）中与中枢硬脑膜敏感三叉血管神经元的下游通讯，从而在偏头痛中发挥治疗作用。本研究通过评估皮质扩散性抑制（CSD）对 SPV 中硬脑膜敏感神经元的激活和敏化作用，来研究 onabotA 的作用机制。这是我们最近关于 onabotA 对周围三叉血管神经元的激活和敏化作用的研究的后续。
在麻醉的雄性和雌性大鼠中，使用单细胞记录来评估颅外注射 onabotA（五次注射，每次一个单位，在 5 μl 盐水中稀释，沿着矢状缝（两个注射部位）和人字缝（两个注射部位）进行）与载体对 CSD 诱导的 SPV 中高阈值（HT）和宽动态范围（WDR）硬脑膜敏感神经元的激活和敏化作用的影响。
对预处理 onabotA 对 CSD 诱导的 SPV 中中枢三叉血管神经元的激活和敏化作用的单细胞分析表明，这种神经毒素能够防止 WDR 神经元的激活和敏化（对照组中 4/16（25%）激活神经元与治疗组中 13/20（65%）激活神经元相比，= 0.022，Fisher 精确检验）。相比之下，onabotA 预处理对 CSD 诱导的 HT 神经元的激活和敏化作用没有影响，对其激活也没有影响（对照组中 12/18（67%）激活神经元与治疗组中 12/18（67%）激活神经元相比，= 0.14，Fisher 精确检验）。关于敏化作用，我们发现，onabotA 预处理可防止 WDR 和 HT 神经元对皮肤机械刺激的反应增强（即反映中枢敏化的反应）。在对照组而不是治疗组的 WDR 神经元中，对刷（0.004 对 0.007）、压力（= 0.002 对 = 0.79）和捏（= 0.007 对 0.79）的反应在 CSD 后两小时显著增加。同样，在对照组而不是治疗组的 HT 神经元中，对刷（0.002 对 0.79）、压力（= 0.002 对 = 0.72）和捏（= 0.0006 对 = 0.28）的反应在 CSD 后两小时显著增加。出乎意料的是，onabotA 预处理可防止 WDR 和 HT 神经元对硬脑膜机械刺激的反应增强（通常反映外周敏化）。在对照组与治疗组的 WDR 和 HT 神经元中，对硬脑膜刺激的反应增强分别为 70%对 25%（= 0.017）和 78%对 27%（= 0.017）。
onabotA 能够防止 WDR 神经元的激活和敏化，这归因于其对无髓 C 纤维的优先抑制作用。onabotA 不能防止 HT 神经元的激活，这归因于其对薄髓 Aδ 纤维的抑制作用较弱。这些发现为 onabotA 和降钙素基因相关肽信号中和药物的作用机制提供了进一步的临床前证据。
