Qian Jie, Mummalaneni Shobha, Grider John R, Damaj M Imad, Lyall Vijay
Physiology and Biophysics Virginia Commonwealth University, Richmond, VA, United States of America.
Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, United States of America.
PLoS One. 2018 Jan 2;13(1):e0190465. doi: 10.1371/journal.pone.0190465. eCollection 2018.
Nicotine evokes chorda tympani (CT) taste nerve responses and an aversive behavior in Trpm5 knockout (KO) mice. The agonists and antagonists of nicotinic acetylcholine receptors (nAChRs) modulate neural and behavioral responses to nicotine in wildtype (WT) mice, Trpm5 KO mice and rats. This indicates that nicotine evokes bitter taste by activating a Trpm5-dependent pathway and a Trpm5-independent but nAChR-dependent pathway. Rat CT responses to ethanol are also partially inhibited by nAChR blockers, mecamylamine and dihydro-β-erythroidine. This indicates that a component of the bitter taste of ethanol is also nAChR-dependent. However, at present the expression and localization of nAChR subunits has not been investigated in detail in taste receptor cells (TRCs). To this end, in situ hybridization, immunohistochemistry and q-RT-PCR techniques were utilized to localize nAChR subunits in fungiform and circumvallate TRCs in WT mice, Trpm5-GFP transgenic mice, nAChR KO mice, and rats. The expression of mRNAs for α7, β2 and β4 nAChR subunits was observed in a subset of rat and WT mouse circumvallate and fungiform TRCs. Specific α3, α4, α7, β2, and β4 antibodies localized to a subset of WT mouse circumvallate and fungiform TRCs. In Trpm5-GFP mice α3, α4, α7, and β4 antibody binding was observed in a subset of Trpm5-positive circumvallate TRCs. Giving nicotine (100 μg/ml) in drinking water to WT mice for 3 weeks differentially increased the expression of α3, α4, α5, α6, α7, β2 and β4 mRNAs in circumvallate TRCs to varying degrees. Giving ethanol (5%) in drinking water to WT mice induced an increase in the expression of α5 and β4 mRNAs in circumvallate TRCs with a significant decrease in the expression of α3, α6 and β2 mRNAs. We conclude that nAChR subunits are expressed in Trpm5-positive TRCs and their expression levels are differentially altered by chronic oral exposure to nicotine and ethanol.
尼古丁可诱发鼓索神经（CT）味觉神经反应，并在瞬时受体电位阳离子通道蛋白5基因敲除（KO）小鼠中引发厌恶行为。烟碱型乙酰胆碱受体（nAChRs）的激动剂和拮抗剂可调节野生型（WT）小鼠、瞬时受体电位阳离子通道蛋白5基因敲除小鼠和大鼠对尼古丁的神经和行为反应。这表明尼古丁通过激活一条依赖瞬时受体电位阳离子通道蛋白5的途径和一条不依赖瞬时受体电位阳离子通道蛋白5但依赖烟碱型乙酰胆碱受体的途径来诱发苦味。大鼠CT对乙醇的反应也会被烟碱型乙酰胆碱受体阻滞剂美加明和二氢-β-刺桐啶部分抑制。这表明乙醇苦味的一个成分也是依赖烟碱型乙酰胆碱受体的。然而，目前尚未在味觉受体细胞（TRCs）中详细研究烟碱型乙酰胆碱受体亚基的表达和定位。为此，利用原位杂交、免疫组织化学和定量逆转录聚合酶链反应技术在WT小鼠、瞬时受体电位阳离子通道蛋白5绿色荧光蛋白转基因小鼠、烟碱型乙酰胆碱受体基因敲除小鼠和大鼠的菌状乳头和轮廓乳头TRCs中定位烟碱型乙酰胆碱受体亚基。在大鼠和WT小鼠的一部分轮廓乳头和菌状乳头TRCs中观察到了α7、β2和β4烟碱型乙酰胆碱受体亚基mRNA的表达。特异性的α3、α4、α7、β2和β4抗体定位于WT小鼠轮廓乳头和菌状乳头的一部分TRCs。在瞬时受体电位阳离子通道蛋白5绿色荧光蛋白小鼠中，在一部分瞬时受体电位阳离子通道蛋白5阳性的轮廓乳头TRCs中观察到了α3、α4、α7和β4抗体结合。给WT小鼠饮用含尼古丁（100μg/ml）的水3周，不同程度地差异增加了轮廓乳头TRCs中α3、α4、α5、α6、α7、β2和β4 mRNA的表达。给WT小鼠饮用含乙醇（5%）的水会诱导轮廓乳头TRCs中α5和β4 mRNA的表达增加，同时α3、α6和β2 mRNA的表达显著降低。我们得出结论，烟碱型乙酰胆碱受体亚基在瞬时受体电位阳离子通道蛋白5阳性的TRCs中表达，并且它们的表达水平会因长期口服尼古丁和乙醇而发生不同程度的改变。
