Sohal G S, Kumaresan K, Hirano S, Ali M M
Department of Anatomy, Medical College of Georgia, Augusta 30912.
Int J Dev Neurosci. 1991;9(6):563-70. doi: 10.1016/0736-5748(91)90017-g.
There is a normally occurring death of about half of the trochlear motor neurons during development. Early removal of the target muscle results in death of almost all neurons whereas neuromuscular blockade prevents neuron death. The present investigation was undertaken to determine whether the number of central afferent synapses on motor neurons is altered under conditions which either accentuate cell loss or rescue neurons. The sole peripheral target of innervation of the trochlear motor neurons, the superior oblique muscle, was extirpated in duck embryos before the motor axon outgrowth begins. The neuromuscular blockade was achieved by application of paralyzing dosages of alpha bungarotoxin on to the vascularized chorioallantoic membrane. This treatment began prior to the onset of cell death and embryos were treated daily throughout the period of cell death. Brains were processed for electron microscopy and quantitative observations were made on synapses at the onset, during the period of, and at the end of cell death. It was found that there was no significant difference in the number of synapses on neurons following target removal, following neuromuscular blockade, and those developing normally. This observation indicates that the number of central afferent synapses on cell soma is not altered under conditions which either decrease or increase neuron survival. These results suggest that the synapse number per se may not be directly involved in the process of naturally occurring cell death. The results also suggest that the number of synapses on trochlear motor neurons is independent of interactions with the target.
在发育过程中，约一半的滑车运动神经元会正常死亡。早期切除靶肌肉会导致几乎所有神经元死亡，而神经肌肉阻滞可防止神经元死亡。本研究旨在确定在加剧细胞死亡或挽救神经元的条件下，运动神经元上的中枢传入突触数量是否会发生改变。在鸭胚运动轴突开始长出之前，将滑车运动神经元唯一的外周靶标上斜肌切除。通过将麻痹剂量的α-银环蛇毒素应用于血管化的尿囊绒膜来实现神经肌肉阻滞。这种治疗在细胞死亡开始之前开始，并且在细胞死亡期间每天对胚胎进行治疗。对大脑进行电子显微镜处理，并在细胞死亡开始时、期间和结束时对突触进行定量观察。结果发现，在切除靶标、进行神经肌肉阻滞后以及正常发育的神经元上，突触数量没有显著差异。这一观察结果表明，在减少或增加神经元存活的条件下，细胞体上的中枢传入突触数量不会改变。这些结果表明，突触数量本身可能不直接参与自然发生的细胞死亡过程。结果还表明，滑车运动神经元上的突触数量与和靶标的相互作用无关。
