Schwarz C, Thier P
Sektion für Visuelle Sensomotorik, Neurologische Universitätsklinik Tübingen, Germany.
J Neurosci. 1995 May;15(5 Pt 1):3475-89. doi: 10.1523/JNEUROSCI.15-05-03475.1995.
Cortical afferents transferring information destined for the cerebellum terminate in the pontine nuclei (PN) in a divergent and patchy fashion. We investigated whether the form of dendritic fields of pontine projection neurons which are postsynaptic to the cortical afferents are related to this patchy pattern. To this end we used a triple combination of (1) retrograde labeling (injection of Fluorogold into the brachium pontis), (2) anterograde labeling [injection of Dil into cortical areas A17 and Sml(forelimb)], and (3) subsequent intracellular fills of identified projection neurons (Lucifer yellow) in slightly fixed slices of pontine brainstem. In 64 projection neurons whose somata were located within 160 microns of the border defined by cortical afferent fields, most of the dendritic trees were found to respect the border. Strikingly, proximal dendrites which were oriented toward the border often bent in order to avoid the boundary. This observation was supported by a quantitative analysis. It revealed that overlap areas of dendritic fields with the neighboring compartment were significantly smaller than those of hypothetical, radially organized dendritic fields of the same size, indicating that the dendritic fields are indeed confined to single compartments. In a second series of experiments, double injections of the anterograde tracers Dil and DiAsp into adjacent sites within one cortical area (A17 or Sml) were made in order to test if the topology of the cortical map is preserved within individual pontine compartments. This, however, does not seem to be the case, since the terminal fields displayed a complex pattern of overlap and nonoverlap rather than a consistent shift of terminal fields expected in the case of preserved topology. The results of the present study are consistent with the view that pontine modules independently process information from different parts of individual cortical areas. We suggest that this characteristic property of the corticopontine projection system might be the morphological basis of the well established fact that somatotopically continuous sensory maps in the cortex are transformed into maps at the level of the cerebellar cortex, showing a fractured somatotopy.
传递信息至小脑的皮质传入神经以发散且呈斑块状的方式终止于脑桥核（PN）。我们研究了作为皮质传入神经突触后神经元的脑桥投射神经元的树突野形态是否与这种斑块状模式有关。为此，我们采用了以下三重组合方法：（1）逆行标记（将荧光金注入脑桥臂），（2）顺行标记[将Dil注入皮质区域A17和Sml（前肢）]，以及（3）随后在脑桥脑干的轻度固定切片中对已识别的投射神经元进行细胞内填充（路西法黄）。在64个胞体位于由皮质传入神经野定义的边界160微米范围内的投射神经元中，发现大多数树突树遵循该边界。令人惊讶的是，朝向边界的近端树突常常弯曲以避开边界。这一观察结果得到了定量分析的支持。分析表明，树突野与相邻区域的重叠面积明显小于相同大小的假设性径向组织树突野的重叠面积，这表明树突野确实局限于单个区域。在第二系列实验中，为了测试皮质图谱的拓扑结构是否在单个脑桥区域内得以保留，我们在一个皮质区域（A17或Sml）内的相邻位点进行了顺行示踪剂Dil和DiAsp的双重注射。然而，情况似乎并非如此，因为终末野呈现出复杂的重叠和非重叠模式，而不是在拓扑结构保留的情况下预期的终末野的一致移位。本研究结果与以下观点一致，即脑桥模块独立处理来自单个皮质区域不同部分的信息。我们认为，皮质 - 脑桥投射系统的这一特性可能是以下既定事实的形态学基础：皮质中躯体感觉连续的感觉图谱在小脑皮质水平转变为图谱，呈现出破碎的躯体定位。
