Girard Brigitte, Couesnon Aurélie, Girard Emmanuelle, Molgó Jordi
Service d'Ophtalmologie, Hôpital Tenon, Sorbonne Université, Université Pierre et Marie Curie, 4 rue de la Chine, 75020 Paris, France.
Hôpital Privé Armand Brillard, 3. Avenue Watteau, 94130 Nogent sur Marne, France.
Toxins (Basel). 2024 Nov 24;16(12):506. doi: 10.3390/toxins16120506.
Botulinum neurotoxin type-A (BoNT/A), which blocks quantal acetylcholine (ACh) release at the neuromuscular junction (NMJ), has demonstrated its efficacy in the symptomatic treatment of blepharospasm. In 3.89% of patients treated for blepharospasm at Tenon Hospital, BoNT/A was no longer effective in relieving the patient's symptoms, and a partial upper myectomy of the muscle was performed. We used surgical waste samples from 14 patients treated with repeated injections of either abobotulinumtoxinA (Dysport) or incobotulinumtoxinA (Xeomin). These muscle fragments were compared to others from 4 normal subjects, naïve of BoNT/A. The morphological study was performed blinded to the BoNT/A treatment and between treated and control samples. Neuromuscular specimens analyzed by confocal laser scanning microscopy, using fluorescent staining and immune-labeling of presynaptic proteins, revealed that the pattern of innervation (e.g., polyneuronal and convergent innervation), the muscle nicotinic ACh receptors (nAChRs), and the NMJs exhibited marked differences in BoNT/A-treated muscles (regardless of the toxin clinically used), with respect to controls. BoNT/A-treated junctions exhibited profuse polyneuronal innervation in which 2-6 axons innervated 74.84% of single muscle fibers, while 99.47% of control junctions were mono-innervated. Another new finding was the stable convergent innervation, in which several motor axons end onto the same endplate. Morphological signs of synapse elimination included the presence of retraction bulbs in axons and nerve terminals and a reduced extension of postsynaptic nAChRs. These outcomes suggest that synapse elimination is altered and raise questions on the origin and factors contributing to the plasticity changes observed and the functioning of NMJs.
A型肉毒杆菌神经毒素(BoNT/A)可阻断神经肌肉接头(NMJ)处的量子化乙酰胆碱(ACh)释放,已在睑痉挛的对症治疗中显示出疗效。在特农医院接受睑痉挛治疗的患者中,有3.89%的患者使用BoNT/A后不再能有效缓解症状,于是对其进行了部分上睑肌切除术。我们使用了14例反复注射阿柏西普肉毒毒素A(Dysport)或因卡肉毒毒素A(Xeomin)治疗患者的手术废弃物样本。将这些肌肉碎片与4例未接触过BoNT/A的正常受试者的肌肉碎片进行比较。形态学研究在对BoNT/A治疗不知情的情况下,在治疗样本和对照样本之间进行。通过共聚焦激光扫描显微镜分析神经肌肉标本,使用荧光染色和突触前蛋白的免疫标记,结果显示,与对照组相比,在接受BoNT/A治疗的肌肉中(无论临床上使用何种毒素),神经支配模式(如多神经元和汇聚性神经支配)、肌肉烟碱型ACh受体(nAChRs)和神经肌肉接头均表现出显著差异。接受BoNT/A治疗的接头表现出丰富的多神经元神经支配,其中2 - 6条轴突支配74.84%的单根肌纤维,而99.47%的对照接头为单神经元支配。另一个新发现是稳定的汇聚性神经支配,即几条运动轴突终止于同一个终板。突触消除的形态学标志包括轴突和神经末梢中出现收缩球以及突触后nAChRs的延伸减少。这些结果表明突触消除发生了改变,并引发了关于观察到的可塑性变化的起源和促成因素以及神经肌肉接头功能的问题。