Gan W B, Macagno E R
Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
J Neurosci. 1995 May;15(5 Pt 1):3254-62. doi: 10.1523/JNEUROSCI.15-05-03254.1995.
Pioneer neurons are known to guide later developing neurons during the initial phases of axonal outgrowth. To determine whether they are also important in the formation of terminal fields by the follower cells, we studied the role of a putative leech pioneer neuron, the pressure-sensitive (PD) neuron, in the establishment of other neurons' peripheral arbors. The PD neuron has a major axon that exits from its segmental ganglion to grow along the dorsal-posterior (DP) nerve to the dorsal body wall, where it arborizes extensively mainly in its own segment. It also has two minor axons that project to the two adjacent segments but branch to a lesser degree. We found that the peripheral projections of several later developing neurons, including the AP motor neuron and the TD sensory neuron, followed, with great precision, the major axon and peripheral arbor of the consegmental PD neuron, up to its fourth-order branches. When a PD neuron was ablated before it had grown to the body wall, the AP and TD axons grew normally toward and reached the target area, but then formed terminal arbors that were greatly reduced in size and abnormal in morphology. Further, if the ablation of a PD neuron was accompanied by the induction, in the same segment, of greater outgrowth of the minor axon of a PD neuron from the adjacent segment, the arbors of the same AP neurons grew along these novel PD neuron branches. These results demonstrate that the peripheral arbor of a PD neuron is a both necessary and sufficient template for the formation of normal terminal fields by certain later growing follower neurons.
已知先驱神经元在轴突生长的初始阶段引导后期发育的神经元。为了确定它们在跟随细胞形成终末场的过程中是否也很重要，我们研究了一种假定的水蛭先驱神经元——压力敏感（PD）神经元在其他神经元外周分支形成中的作用。PD神经元有一条主要轴突，从其节段神经节发出，沿着背-后（DP）神经向背侧体壁生长，在那里它主要在自己的节段内广泛分支。它还有两条较小的轴突，伸向相邻的两个节段，但分支程度较小。我们发现，包括AP运动神经元和TD感觉神经元在内的几个后期发育神经元的外周投射，非常精确地跟随同节段PD神经元的主要轴突和外周分支，直至其四阶分支。当一个PD神经元在生长到体壁之前被切除时，AP和TD轴突正常地向目标区域生长并到达，但随后形成的终末分支在大小上大大减小且形态异常。此外，如果在切除一个PD神经元的同时，在同一节段诱导相邻节段的PD神经元较小轴突有更大的生长，相同AP神经元的分支会沿着这些新的PD神经元分支生长。这些结果表明，PD神经元的外周分支对于某些后期生长的跟随神经元形成正常的终末场既是必要的也是充分的模板。
