Jacquin Mark F, Arends Joop J A, Renehan William E, Waite Phil M E, Shortland Peter J
Department of Neurology, Washington University School of Medicine , St Louis, MO , USA .
Somatosens Mot Res. 2015;32(1):8-20. doi: 10.3109/08990220.2014.937414. Epub 2014 Jul 14.
Single whiskers are topographically represented in the trigeminal (V) nucleus principalis (PrV) by a set of cylindrical aggregates of primary afferent terminals and somata (barrelettes). This isomorphic pattern is transmitted to the thalamus and barrel cortex. However, it is not known if terminals in PrV from neighboring whiskers interdigitate so as to violate rules of spatial parcellation predicted by barrelette borders; nor is it known the extent to which higher order inputs are topographic. The existence of inter-whisker arbor overlap or diffuse higher order inputs would demand additional theoretical principles to account for single whisker dominance in PrV cell responses. In adult rats, first, primary afferent pairs responding to the same or neighboring whiskers and injected with Neurobiotin or horseradish peroxidase were rendered brown or black to color-code their terminal boutons. When collaterals from both fibers appeared in the same topographic plane through PrV, the percentage of the summed area of the two arbor envelopes that overlapped was computed. For same-whisker pairs, overlap was 5 ± 6% (mean ± SD). For within-row neighbors, overlap was 2 ± 5%. For between-row neighbors, overlap was 1 ± 4%. Second, the areas of whisker primary afferent arbors and their corresponding barrelettes in the PrV were compared. In the transverse plane, arbor envelopes significantly exceeded the areas of cytochrome oxidase-stained barrelettes; arbors often extended into neighboring barrelettes. Third, bulk tracing of the projections from the spinal V subnucleus interpolaris (SpVi) to the PrV revealed strict topography such that they connect same-whisker barrelettes in the SpVi and PrV. Thus, whisker primary afferents do not exclusively project to their corresponding PrV barrelette, whereas higher order SpVi inputs to the PrV are precisely topographic.
单根触须在三叉神经（V）主核（PrV）中通过一组初级传入终末和胞体的圆柱形聚集体（小桶柱）进行拓扑表征。这种同构模式会传递至丘脑和桶状皮层。然而，尚不清楚来自相邻触须的PrV终末是否相互交错，从而违反由小桶柱边界预测的空间分隔规则；也不清楚高阶输入在多大程度上具有拓扑结构。触须间树突重叠或弥散性高阶输入的存在将需要额外的理论原则来解释PrV细胞反应中的单根触须优势。在成年大鼠中，首先，对响应相同或相邻触须并注射神经生物素或辣根过氧化物酶的初级传入纤维对进行染色，使其呈棕色或黑色，以便对其终末小体进行颜色编码。当来自两根纤维的侧支通过PrV出现在同一拓扑平面时，计算两个树突包络总面积的重叠百分比。对于响应同一触须的纤维对，重叠率为5±6%（平均值±标准差）。对于同一排相邻触须的纤维对，重叠率为2±5%。对于不同排相邻触须的纤维对，重叠率为1±4%。其次，比较了触须初级传入纤维树突及其在PrV中相应小桶柱的面积。在横切面上，树突包络明显超过细胞色素氧化酶染色的小桶柱面积；树突常常延伸到相邻的小桶柱中。第三，对从脊髓V极间亚核（SpVi）到PrV的投射进行整体追踪，结果显示出严格的拓扑结构，即它们连接SpVi和PrV中响应同一触须的小桶柱。因此，触须初级传入纤维并非仅投射到其相应的PrV小桶柱，而SpVi对PrV的高阶输入则具有精确的拓扑结构。
