Extension and retraction of axonal projections by some developing neurons in the leech depends upon the existence of neighboring homologues. I. The HA cells.
Extension and retraction of axonal projections by some developing neurons in the leech depends upon the existence of neighboring homologues. I. The HA cells.
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水蛭中一些发育中的神经元的轴突投射的延伸和收缩取决于邻近同源物的存在。
DOI：
10.1002/neu.480180105
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Macagno,ER
中科院分区：
文献类型：
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作者：
Gao,WQ;Macagno,ER
为了评估我们之前发现（Gao和Macagno， 1987）的普遍性，即节段同源物在心脏附件HA神经元轴突投射模式的建立中发挥作用，我们将研究扩展到另外两个已确定的水蛭神经元：前塔（AP）神经元和环竖立（AE）运动神经元。在水蛭腹侧神经索第1至第20节节节（SG1至SG20）中发现双侧AP神经元对。所有AP神经元最初向对侧外周延伸轴突投射，并沿着对侧节间结缔组织神经向前后相邻神经节延伸纵向投射。尽管所有AP神经元在动物的一生中都维持外周投射，但除了两个节段外，所有节段的纵向投射都消失了：SG1的AP神经元保持其前投射并延伸到头神经节，SG20的AP神经元保持其后投射并延伸到SG21和尾神经节。然而，当单个AP神经元在神经突开始萎缩之前沿神经索的任何地方被删除时，其纵向突起被相邻神经节中的同侧同源物保留。恢复的过程似乎接管了被删除的神经元的投射。在神经索同侧两个或更多AP神经元从相邻神经节缺失的情况下，对侧同源物有时会将投影延伸到同侧或两侧的外周。当我们从中体神经节中删除单个AE神经元时，我们得到了类似的结果。因此，我们对三种不同的已识别神经元的实验一致表明，所有神经节的初始投射模式是相同的，但相邻神经节中同源物的存在导致一些初始投射被修剪。这种依赖同源物的过程收缩的结果是，通常缺乏邻近同源物的神经元将具有不同于那些有邻近同源物的神经元的投射模式。
To assess the generality of our previous finding (Gao and Macagno, 1987) that segmental homologues play a role in the establishment of the pattern of axonal projections of the heart accesory HA neurons, we have extended our studies to two other identified leech neurons: the anterior pagoda (AP) neurons and the annulus erector (AE) motor neurons. Bilateral pairs of AP neurons are found in the first through the twentieth segmental ganglia (SG1 through SG20) of the leech ventral nerve cord. All AP neurons initially extend axonal projections to the contralateral periphery as well as longitudinal projections along the contralateal interganglionic connective nerves toward anterior and posterior neighboring ganglia. Although the peripheral projections are maintained by all AP neurons throughout the life of the animal, the longitudinal projections disappear in all but two segments: the AP neurons in SG1 maintain their anterior projections and extend them into the head ganglion, and those in SG20 maintain their posterior projections and extend them into SG21 and the tail ganglion. When single AP neurons are delted anywhere along the nerve cord before processes begin to atrophy, however, the longtudinal projections are retained by their ipsilateral homologues in adjacent ganglia. The rescued processes appear to take over the projections of the deleted neurons. In cases where two or more AP neurons on the same side of the nerve cord are deleted from adjacent ganglia, a contralateral homologue sometimes extends projections to the periphery ipsilaterally or on both sides. We obtained similar results when we deleted single AE neurons from midbody ganglia. Thus, our experiments with three different identified neurons consistently show that the initial pattern of projections is the same in all ganglia, but that the existence of homologues in adjacent ganglia leads to the pruning of some of the initial projections. A consequence of this homologue‐dependent process retraction is that neurons normally lacking neighboring homologues will have patterns of projections different from those neurons that do have such neighbors.