Genetic approach to trace construction of taste neuronal circuitries

为了深入了解味觉信息是如何通过大脑中特定的核继电器处理和整合的，并解决味觉神经元回路构建的潜在机制，我们应用遗传学方法，通过在小鼠的苦味或甜味感受器细胞中选择性地表达跨突触示踪物tWGA-DsRed来描绘苦味和甜味的神经元回路。从苦味或甜味感受器细胞转移的tWGA-DsRed的空间分布在整个大脑的连续冠状切片上被检测到。分析tWGA-DsRed标记神经元在全脑三维图像中的位置，通过拼接从连续切片图像中提取的脑结构来重建全脑图像。尽管标记密度可能会受到示踪剂的运输和降解效率的影响，这可能会因神经元类型而异，但标记…的神经元与苦味感受器细胞相比，tWGA-DsRed更多地位于孤束核和味觉皮质的前部。在成年小鼠的味觉皮质，两个品系的tWGA-DsRed标记神经元的散在区域沿前后轴线部分重叠。这种遗传学方法对于研究味觉神经回路的构建和完善以调节味觉辨别的细胞和分子方面可能是有价值的。在甜味神经回路的发育阶段，位于孤束核和味觉皮质最前部的神经元最初接受来自甜味感受器细胞的tWGA-DsRed，显示出甜味和苦味输入之间的明显分离。结果表明，预先指定的神经元对可能选择性地构建神经元回路来处理苦味或甜味信息。较少

To gain insight into how gustatory information is processed and integrated by the specific nuclear relays in the brain, and to address the mechanisms underlying the construction of taste neuronal circuitries, we applied a genetic approach to delineate the neuronal circuitries of bitter and sweet taste by selectively expressing the transsynaptic tracer, tWGA-DsRed, in either bitter-or sweet-responsive taste receptor cells in mice. The spatial distribution of tWGA-DsRed that was transferred from either bitter-or sweet-responsive taste receptor cells was detected in the serial coronal sections of the whole brain. Locations of tWGA-DsRed-labeled neurons were analyzed in three-dimensional images of the whole brain, which were reconstructed by assembling the brain structures extracted from the serial section images. Although the labeling density is likely to be influenced by the efficiencies of transport and degradation of the tracer, which may vary among neuronal types, the neurons labeled … More by tWGA-DsRed that was transferred from sweet-responsive taste receptor cells were located in the more anterior regions of both the solitary tract nuclei and the gustatory cortex, compared with those from bitter-responsive taste receptor cells. In the gustatory cortex of adult mice, the dispersed areas of tWGA-DsRed-labeled neurons in two strains appeared to partly overlap along the anterior-posterior axis. This genetic approach may be valuable for investigating the cellular and molecular aspects underlying the construction and refinement of taste neuronal circuitries to mediate taste discrimination. During the developmental stages of sweet taste neuronal circuitries, the neurons located in the most anterior parts of both the solitary tract nuclei and the gustatory cortex initially received tWGA-DsRed originating from sweet-responsive taste receptor cells, showing clear segregation between sweet and bitter inputs. The results suggest that the pre-specified neuron pairs may selectively construct the neuronal circuitries to process either bitter or sweet taste information. Less