Forelimb amputation-induced reorganization in the ventral posterior lateral nucleus (VPL) provides a substrate for large-scale cortical reorganization in rat forepaw barrel subfield (FBS).
Forelimb amputation-induced reorganization in the ventral posterior lateral nucleus (VPL) provides a substrate for large-scale cortical reorganization in rat forepaw barrel subfield (FBS).
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DOI：
10.1016/j.brainres.2014.07.022
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发表时间：
2014-10-02
期刊：
影响因子：
2.9
通讯作者：
Waters RS
中科院分区：
文献类型：
--
作者：
Li CX;Chappell TD;Ramshur JT;Waters RS
在这项研究中，我们研究了腹侧后外侧核(VPL)作为前肢截肢后初级躯体感觉皮质(SI)前爪桶状亚区(FBS)大规模皮质重组的可能底物的作用。此前，我们曾报道，年轻成年大鼠截肢前肢6周后，来自肩部的新输入信号在整个FBS中表达，很可能起源于皮质下。对前肢截肢后1~30周的楔状核(CN)的后续检查表明，CN在皮质重组中的作用不大，从而导致了对VPL的研究。作为第一步，我们利用电生理记录在前肢完整的成年大鼠(n=8)中定位了VPL的身体表征，特别是前爪和肩部的表征，表明VPL是有组织的躯体结构。接下来，我们用刺激和记录技术在正常大鼠(n=5)上观察了(A)从前肢和肩部到SI的投射模式，(B)从前爪和肩部到VPL的投射模式，以及(C)从VPL的前爪和肩部到SI的前肢和肩部的投射模式。结果表明，这些投影具有窄聚焦和同伦的特点。然后利用电生理记录对截肢后7~24周的幼年大鼠(n=5)的前肢前爪代表进行定位。在每个时间段，在VPL的前掌传入区域观察到新的来自肩部的输入。为了确定去传入前爪VPL中的新的肩部输入是否投射到去传入的FBS中的新的肩部部位，我们研究了2只前肢截肢大鼠的丘脑皮质通路。刺激去传入的FBS的一个新的肩部部位反向激活了VPL中前前爪区域的一个细胞；然而，在SI的去传入区域之外的原始肩部代表中的一个部位的类似刺激并不激活前前爪VPL中的细胞。这些结果表明，去传入的FBS的新的肩部输入来自VPL的前前爪区的细胞。在最后一步中，我们利用解剖示踪、刺激和记录技术，在9只前肢正常的大鼠上，观察了从中央核的肩部和前爪感受野区发出的楔丘脑通路，以确定肩区投射是否可能为前爪VPL提供了一个可能的肩部输入来源。将生物素化葡聚糖胺(BDA)注射到中央核团内生理定位的肩部反应部位，VPL中肩部密集标记的轴突终末，但也向前掌VPL发出细小的侧支。此外，给予前爪VPL的微刺激可反向激活CN中肩部感受区的细胞。这些结果表明，前肢正常大鼠的前爪VPL也接受来自CN中的肩部感受点的输入，这些感受点是潜伏的或阈值下的。然而，我们推测，截肢后，这些潜在的肩部输入得到表达，可能是由于网状核(RTN)对GABA抑制的下调。这些结果综合起来，表明VPL为前肢截肢后的大规模皮质重组提供了底物。
In this study, we examined the role of the ventral posterior lateral nucleus (VPL) as a possible substrate for large-scale cortical reorganization in the forepaw barrel subfield (FBS) of primary somatosensory cortex (SI) that follows forelimb amputation. Previously, we reported that, 6 weeks after forelimb amputation in young adult rats, new input from the shoulder becomes expressed throughout the FBS that quite likely has a subcortical origin. Subsequent examination of the cuneate nucleus (CN) 1 to 30 weeks following forelimb amputation showed that CN played an insignificant role in cortical reorganization and led to the present investigation of VPL. As a first step, we used electrophysiological recordings in forelimb intact adult rats (n=8) to map the body representation in VPL with particular emphasis on the forepaw and shoulder representations and showed that VPL was somatotopically organized. We next used stimulation and recording techniques in forelimb intact rats (n=5) and examined the pattern of projection (a) from the forelimb and shoulder to SI, (b) from the forepaw and shoulder to VPL, and (c) from sites in the forepaw and shoulder representation in VPL to forelimb and shoulder sites in SI. The results showed that the projections were narrowly focused and homotopic. Electrophysiological recordings were then used to map the former forepaw representation in forelimb amputated young adult rats (n=5) at 7 to 24 weeks after amputation. At each time period, new input from the shoulder was observed in the deafferented forepaw region in VPL. To determine whether the new shoulder input in the deafferented forepaw VPL projected to a new shoulder site in the deafferented FBS, we examined the thalamocortical pathway in 2 forelimb-amputated rats. Stimulation of a new shoulder site in deafferented FBS antidromically-activated a cell in the former forepaw territory in VPL; however, similar stimulation from a site in the original shoulder representation, outside the deafferented region, in SI did not activate cells in the former forepaw VPL. These results suggest that the new shoulder input in deafferented FBS is relayed from cells in the former forepaw region in VPL. In the last step, we used anatomical tracing and stimulation and recording techniques in forelimb intact rats (n=9) to examine the cuneothalamic pathway from shoulder and forepaw receptive field zones in CN to determine whether projections from the shoulder zone might provide a possible source of shoulder input to forepaw VPL. Injection of biotinylated dextran amine (BDA) into physiologically identified shoulder responsive sites in CN densely labeled axon terminals in the shoulder representation in VPL, but also gave off small collateral branches into forepaw VPL. In addition, microstimulation delivered to forepaw VPL antidromically-activated cells in shoulder receptive field sites in CN. These results suggest that forepaw VPL also receives input from shoulder receptive sites in CN that are latent or subthreshold in forelimb intact rats. However, we speculate that following amputation these latent shoulder inputs become expressed, possibly as a down-regulation of GABA inhibition from the reticular nucleus (RTN). These results, taken together, suggest that VPL provides a substrate for large-scale cortical reorganization that follows forelimb amputation.
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