Section of Oral Neuroscience, Graduate School of Dental Science, Kyushu University, Fukuoka 812-8582, Japan.
BMC Neurosci. 2009 Dec 22;10:152. doi: 10.1186/1471-2202-10-152.
The peptide gurmarin is a selective sweet response inhibitor for rodents. In mice, gurmarin sensitivity differs among strains with gurmarin-sensitive C57BL and gurmarin-poorly-sensitive BALB strains. In C57BL mice, sweet-responsive fibers of the chorda tympani (CT) nerve can be divided into two distinct populations, gurmarin-sensitive (GS) and gurmarin-insensitive (GI) types, suggesting the existence of two distinct reception pathways for sweet taste responses. By using the dpa congenic strain (dpa CG) whose genetic background is identical to BALB except that the gene(s) controlling gurmarin sensitivity are derived from C57BL, we previously found that genetically-elevated gurmarin sensitivity in dpa CG mice, confirmed by using behavioral response and whole CT nerve response analyses, was linked to a greater taste cell population co-expressing sweet taste receptors and a G(alpha)- protein, G(alpha)--gustducin. However, the formation of neural pathways from the increased taste cell population to nerve fibers has not yet been examined.
Here, we investigated whether the increased taste cell population with G(alpha)--gustducin-coupled sweet receptors would be associated with selective increment of GS fiber population or nonselective shift of gurmarin sensitivities of overall sweet-responsive fibers by examining the classification of GS and GI fiber types in dpa CG and BALB mice. The results indicated that dpa CG, like C57BL, possess two distinct populations of GS and GI types of sweet-responsive fibers with almost identical sizes (dpa CG: 13 GS and 16 GI fibers; C57BL: 16 GS and 14 GI fibers). In contrast, BALB has only 3 GS fibers but 18 GI fibers. These data indicate a marked increase of the GS population in dpa CG.
These results suggest that the increased cell population expressing T1r2/T1r3/G(alpha)--gustducin in dpa CG mice may be associated with an increase of their matched GS type fibers, and may form the distinct GS sweet reception pathway in mice. G(alpha)--gustducin may be involved in the GS sweet reception pathway and may be a key molecule for links between sweet taste receptors and cell type-specific-innervation by their matched fiber class.
肽gurmarin 是一种选择性的甜味反应抑制剂，对啮齿动物有效。在小鼠中，gurmarin 敏感性因品系而异，gurmarin 敏感的 C57BL 和 gurmarin 敏感性差的 BALB 品系就是很好的例子。在 C57BL 小鼠中，鼓索神经（CT）的甜味反应纤维可分为两种不同的群体，即 gurmarin 敏感型（GS）和 gurmarin 不敏感型（GI），这表明甜味反应存在两种不同的接受途径。通过使用 dpa 近交系（dpa CG），其遗传背景与 BALB 相同，只是控制 gurmarin 敏感性的基因来自 C57BL，我们之前发现，dpa CG 小鼠的遗传上升高的 gurmarin 敏感性，通过行为反应和整个 CT 神经反应分析得到证实，与表达甜味受体和 G 蛋白（Gα）- gustducin 的更大的味细胞群体有关。然而，从增加的味细胞群体到神经纤维的神经通路的形成尚未得到检查。
在这里，我们通过检查 dpa CG 和 BALB 小鼠中 GS 和 GI 纤维类型的分类，研究了具有甜味受体偶联的 Gα-gustducin 的增加的味细胞群体是否与 GS 纤维群体的选择性增加或整体甜味反应纤维的 gurmarin 敏感性的非选择性转变有关。结果表明，dpa CG 与 C57BL 一样，具有两种不同的甜味反应纤维的 GS 和 GI 类型群体，其大小几乎相同（dpa CG：13 个 GS 和 16 个 GI 纤维；C57BL：16 个 GS 和 14 个 GI 纤维）。相比之下，BALB 只有 3 个 GS 纤维，但有 18 个 GI 纤维。这些数据表明 dpa CG 中 GS 群体明显增加。
这些结果表明，dpa CG 小鼠中表达 T1r2/T1r3/Gα-gustducin 的增加的细胞群体可能与他们匹配的 GS 型纤维的增加有关，并且可能在小鼠中形成独特的 GS 甜味接受途径。Gα-gustducin 可能参与 GS 甜味接受途径，并且可能是甜味受体与细胞类型特异性支配的匹配纤维类之间的联系的关键分子。
