LaMotte C C, Kapadia S E
Section of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut 06510.
J Comp Neurol. 1993 Apr 1;330(1):83-94. doi: 10.1002/cne.903300107.
We have previously demonstrated sprouting of small diameter saphenous afferents, labelled with wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) and (HRP), into the sciatic territory of the adult rat superficial dorsal horn following destruction of sciatic afferents by injection of the sciatic nerve with pronase (a combination of proteolytic enzymes). In the present experiments, we examined the response of myelinated saphenous axons, which terminate in lamina I and the deep dorsal horn (laminae III-V) under the same conditions, with the tracer B subunit of cholera toxin conjugated to HRP (B-HRP) which specifically labels myelinated primary afferents when injected into a peripheral somatic nerve. We also examined changes in the nucleus gracilis, another site of sciatic degeneration and a target of saphenous afferents. Four months after injection of the pronase, the area of label determined by measurement of the width of the saphenous territory in lamina III was expanded by 24% on the pronase side. Since there was also expansion throughout the deep dorsal horn, the area measured by tracing the labelled region in transverse sections was actually twice that of the control side, and the intensity of labelling within the traced area increased by 18%. There was no change in grey matter area due to the lesion. The traced area of labelling in the nucleus gracilis increased by 40%, and increased in intensity by 17%. The substantia gelatinosa is not normally supplied by B-HRP-labelled afferents, and there was no expansion of these sprouted saphenous afferents into the gelatinosa. These results indicate that myelinated afferents can sprout as vigorously in lamina I and the deep dorsal horn as the small diameter afferents do in the substantia gelatinosa; that there is no invasion of the substantia gelatinosa by the myelinated afferents at least as long as the small diameter afferents also have the opportunity to sprout; and that primary afferents have the potential to sprout at more than one site of termination, i.e., both the dorsal horn and the dorsal column nuclei.
我们之前已经证明，在用链霉蛋白酶（一种蛋白水解酶组合）注射坐骨神经破坏坐骨传入神经后，用与辣根过氧化物酶（HRP）偶联的小麦胚凝集素（WGA-HRP）和（HRP）标记的小直径隐神经传入神经会向成年大鼠浅表背角的坐骨区域发芽。在本实验中，我们在相同条件下，用与HRP偶联的霍乱毒素B亚基（B-HRP）作为示踪剂，研究了终止于I层和深背角（III-V层）的有髓隐神经轴突的反应，当将其注射到外周躯体神经中时，B-HRP可特异性标记有髓初级传入神经。我们还研究了薄束核的变化，薄束核是坐骨神经退变的另一个部位，也是隐神经传入神经的靶标。注射链霉蛋白酶四个月后，通过测量III层隐神经区域的宽度确定的标记区域在链霉蛋白酶侧扩大了24%。由于整个深背角也有扩大，通过追踪横切面上的标记区域测量的面积实际上是对照侧的两倍，并且追踪区域内的标记强度增加了18%。损伤未导致灰质面积改变。薄束核中追踪的标记区域增加了40%，强度增加了17%。正常情况下，B-HRP标记的传入神经不会供应胶状质，这些发芽的隐神经传入神经也不会扩展到胶状质中。这些结果表明，有髓传入神经在I层和深背角中能够像小直径传入神经在胶状质中一样有力地发芽；至少只要小直径传入神经也有发芽的机会，有髓传入神经就不会侵入胶状质；并且初级传入神经有可能在不止一个终止部位发芽，即背角和背柱核。
