Department of Anatomy, Histology, and Neuroscience, Medical School, Autonoma University of Madrid, c/ Arzobispo Morcillo 2, Madrid, Spain.
Neuroscience. 2009 Nov 10;163(4):1242-54. doi: 10.1016/j.neuroscience.2009.07.065. Epub 2009 Aug 5.
In the rodent trigeminal principal nucleus (Pr5) the barrelette thalamic-projecting neurons relay information from individual whiskers to corresponding contralateral thalamic barreloids. Here we investigated the presence of lateral asymmetries in the dendritic trees of these neurons, and the morphometric changes resulting from input-dependent plasticity in young adult rats. After retrograde labeling with dextran amines from the thalamus, neurons were digitally reconstructed with Neurolucida, and metrically and topologically analyzed with NeuroExplorer. The most unexpected and remarkable result was the observation of side-to-side asymmetries in the barrelette neurons of control rats. These asymmetries more significantly involved the number of low-grade trees and the total dendritic length, which were greater on the left side. Chronic global input loss resulting from infraorbital nerve (IoN) transection, or loss of active touch resulting from whisker clipping in the right neutralized, or even reversed, the observed lateral differences. While results after IoN transection have to be interpreted in the context of partial neuron death in this model, profound bilateral changes were found after haptic loss, which is achieved without inflicting any nerve damage. After whisker trimming, neurons on the left side closely resembled neurons on the right in controls, the natural dendritic length asymmetry being reversed mainly by a shortening of the left trees and a more moderate elongation of the right trees. These results demonstrate that dendritic morphometry is both side- and input-dependent, and that unilateral manipulation of the sensory periphery leads to bilateral morphometric changes in second order neurons of the whisker-barrel system. The presence of anatomical asymmetries in neural structures involved in early stages of somatosensory processing could help explain the expression of sensory input-dependent behavioral asymmetries.
在啮齿动物三叉神经主核（Pr5）中，有纹状体投射神经元将来自各个触须的信息中继到相应的对侧触须纹状体。在这里，我们研究了这些神经元树突的存在侧不对称性，以及年轻成年大鼠输入依赖性可塑性导致的形态变化。在丘脑用葡聚糖胺进行逆行标记后，使用 Neurolucida 对神经元进行数字重建，并使用 NeuroExplorer 进行度量和拓扑分析。最出乎意料和显著的结果是观察到对照组大鼠纹状体神经元的左右不对称。这些不对称性更显著地涉及到低等级树的数量和总树突长度，它们在左侧更大。由于眶下神经（IoN）切断导致的慢性整体输入损失，或由于右侧触须修剪导致的主动触觉丧失，这些观察到的侧差异得到中和，甚至逆转。虽然在这个模型中，IoN 切断后的结果必须在部分神经元死亡的背景下进行解释，但在触觉丧失后发现了深刻的双侧变化，而触觉丧失是在不造成任何神经损伤的情况下实现的。在修剪触须后，左侧神经元与对照组右侧神经元非常相似，自然树突长度不对称主要通过缩短左侧树突和适度延长右侧树突来逆转。这些结果表明，树突形态计量既依赖于侧方，也依赖于输入，单侧感觉外周的操作会导致触须-桶状系统的二级神经元发生双侧形态计量变化。参与躯体感觉处理早期阶段的神经结构中存在解剖学不对称性，可能有助于解释感觉输入依赖性行为不对称性的表达。
