Kramer A P, Kuwada J Y
J Neurosci. 1983 Dec;3(12):2474-86. doi: 10.1523/JNEUROSCI.03-12-02474.1983.
We have charted the embryonic development of the epidermal receptive fields of the PV and PD mechanosensory neurons present in each segmental ganglion of the ventral nerve cord of the glossiphoniid leech Haementeria ghilianii. The receptive field of either of these neurons is established by several peripheral axons, each of which grows into its own skin territory, so that the receptive field is subdivided into a quiltwork of contiguous, mutually exclusive subfields of various sizes. The largest subfield develops first from the primary peripheral axon of the PD or PV neuron. The PD and PV primary axons grow directly to their respective territories and begin to innervate them at approximately the same time (see also Kuwada, J.Y., and A.P. Kramer (1983) J. Neurosci. 3: 2098-2111). The smaller secondary and minor subfields develop later from the secondary and intersegmental peripheral axons, respectively. These axons, too, grow directly to their appropriate skin territories. The arborizations of the peripheral axons expand until the adult receptive field pattern is established late in embryogenesis; they do not appear to initially overgrow and later trim down to the normal boundaries of the adult receptive field. The receptive field of the PV neuron develops from a stereotyped skeletal branching pattern of the peripheral axons that is elaborated in a regular way to form a grid-like pattern that matches the arrangement of muscle fibers in the body wall. Thus, this branching pattern may be the result of axon growth along prespecified pathways, perhaps delineated by the muscles. Throughout embryonic development, as in the adult leech, axon branches of neighboring homologous P neurons overlap considerably, but separate axon branches of the same neuron are virtually non-overlapping. These observations suggest that developing branches of a neuron are excluded from territory occupied by other branches of the same cell, in contrast to branches belonging to different neurons which can occupy the same territory.
我们绘制了光润金线蛭（Haementeria ghilianii）腹神经索各节段神经节中存在的PV和PD机械感觉神经元表皮感受野的胚胎发育过程。这些神经元中任何一个的感受野都由几条外周轴突建立，每条轴突都生长到其自身的皮肤区域，因此感受野被细分为由各种大小的相邻、相互排斥的子区域组成的拼布图案。最大的子区域首先从PD或PV神经元的初级外周轴突发育而来。PD和PV初级轴突直接生长到它们各自的区域，并在大约相同的时间开始支配这些区域（另见Kuwada, J.Y., 和A.P. Kramer (1983) J. Neurosci. 3: 2098 - 2111）。较小的次级和微小子区域分别稍后从次级和节间外周轴突发育而来。这些轴突也直接生长到它们适当的皮肤区域。外周轴突的分支不断扩展，直到在胚胎发育后期建立起成年感受野模式；它们似乎最初不会过度生长，然后再修剪到成年感受野的正常边界。PV神经元的感受野由外周轴突的定型骨骼分支模式发育而来，这种模式以规则的方式细化形成与体壁肌肉纤维排列相匹配的网格状模式。因此，这种分支模式可能是轴突沿着预先确定的路径生长的结果，也许是由肌肉勾勒出来的。在整个胚胎发育过程中，与成年水蛭一样，相邻同源P神经元的轴突分支有相当大的重叠，但同一神经元的不同轴突分支几乎不重叠。这些观察结果表明，与属于不同神经元的分支可以占据同一区域相反，一个神经元的发育分支被排除在同一细胞的其他分支所占据的区域之外。
