Hall G F, Cohen M J
Department of Biology, Yale University, New Haven, Connecticut 06511.
J Neurosci. 1988 Oct;8(10):3584-97. doi: 10.1523/JNEUROSCI.08-10-03584.1988.
We have investigated some of the factors controlling the distribution of axonal and dendritic sprouting following axotomy of a subset of Muller giant interneurons (anterior bulbar cells or ABCs) in the hindbrain of the larval sea lamprey (Petromyzon marinus). Sprouts originated from different sites in the cell depending on the distance of the axonal lesion from the soma. When the axon was cut close to the soma (within 500 microns), the dendritic tips sprouted profusely, whereas the proximal axon stump showed few sprouts and frequently disappeared entirely. Axotomy further from the soma (1000-1400 microns) resulted in less sprouting from the dendrites and more from the axon stump, with the total amount of dendritic plus axonal sprouting remaining constant. Axotomy at sites distant from the soma (1 cm or more) did not result in dendritic sprouting. No sprouts were ever observed emerging from the soma proper or from the axon stump except at the lesion site. Neuritic sprouts from dendrites and axon were similar in their gross morphology. Sprouts resembled axons rather than dendrites whatever their sites of origin; they followed linear, rostrocaudally oriented paths in the "basal plate" region of the hindbrain. Dendritic and axonal sprouts grew both rostrally and caudally within the brain. Either "close" or "distant" axotomy resulted in the retraction of the dendritic tree and of both dendritic and axonal sprouts by several months postaxotomy. Reaxotomy close to the soma 30 d after a distant axotomy accelerated the onset of this evoked dendritic retraction. Reaxotomy close to the soma also induced sprouting significantly sooner than did close axotomy alone. These results suggest that axotomy close to the soma causes axonal regeneration to be shunted into ectopic locations at the dendritic tips. The emerging sprouts then follow guidance cues appropriate for regenerating ABC axons.
我们研究了一些控制海七鳃鳗（Petromyzon marinus）幼体后脑 Müller 巨型中间神经元（前延髓细胞或 ABCs）的一个亚群轴突切断后轴突和树突发芽分布的因素。根据轴突损伤与胞体的距离，芽从细胞的不同部位长出。当轴突在靠近胞体处（500 微米以内）被切断时，树突尖端大量发芽，而近端轴突残端发芽很少，且常常完全消失。在离胞体较远（1000 - 1400 微米）处进行轴突切断，导致树突发芽减少，轴突残端发芽增多，树突和轴突发芽的总量保持不变。在离胞体较远（1 厘米或更远）的部位进行轴突切断，不会导致树突发芽。除了损伤部位外，从未观察到芽从胞体本身或轴突残端长出。来自树突和轴突的神经突芽在大体形态上相似。无论芽的起源部位如何，它们都更像轴突而不是树突；它们在后脑的“基板”区域沿着线性的、头尾方向排列的路径生长。树突和轴突芽在脑内向前和向后生长。无论是“近”轴突切断还是“远”轴突切断，在轴突切断后几个月都会导致树突树以及树突和轴突芽的回缩。在远轴突切断 30 天后，靠近胞体再次进行轴突切断会加速这种诱发的树突回缩的开始。靠近胞体再次进行轴突切断也比单独进行近轴突切断显著更早地诱导发芽。这些结果表明，靠近胞体的轴突切断会导致轴突再生被转移到树突尖端的异位位置。然后，新出现的芽遵循适合 ABC 轴突再生的引导线索。
