Dept. of Anatomy and Neurobiology, Univ. of Tennessee Health Science Center, Memphis, TN 38163, USA.
J Neurophysiol. 2012 Oct;108(8):2179-90. doi: 10.1152/jn.00465.2012. Epub 2012 Jul 25.
We investigated sweet-bitter and umami-bitter mixture taste interactions by presenting sucrose or umami stimuli mixed with quinine hydrochloride (QHCl) while recording single-unit activity of neurons in the parabrachial nucleus (PbN) of urethane-anesthetized C57BL/6J mice. A total of 70 taste-responsive neurons were classified according to which stimulus evoked the greatest net response (36 sucrose-best, 19 NaCl-best, 6 citric acid-best, and 9 QHCl-best). Although no neurons responded best to monopotassium glutamate (MPG) or inosine 5'-monophosphate (IMP), the combination of these two stimuli evoked a synergistic response (i.e., response > 120% of the sum of the component responses) in all sucrose-best and some NaCl-best neurons (n = 43). Adding QHCl to sucrose or MPG + IMP resulted in suppression of the response (responses to mixture < responses to the more effective component) in 41 of 43 synergistic neurons. Neurons showing QHCl suppression were classified into two types: an "MS1" type (n = 27) with suppressed responses both to sucrose and MPG + IMP and an "MS2" type (n = 14) that showed suppressed responses only to sucrose. No neuron displayed suppressed responses to MPG or IMP alone. The suppression ratio (1 - mixture response/sucrose or MPG + IMP response) of sucrose and MPG + IMP in MS1 neurons had a weak positive correlation (r = 0.36). The pattern of reconstructed recording sites of neuron types suggested chemotopic organization in the PbN. Although a peripheral basis for QHCl suppression has been demonstrated, our results suggest that convergence in the PbN plays a role in shaping responses to taste mixtures.
我们通过在给麻醉的 C57BL/6J 小鼠的臂旁核（PbN）记录单个神经元的活动的同时，给蔗糖或鲜味刺激物与盐酸奎宁（QHCl）混合，来研究甜-苦和鲜-苦混合味觉相互作用。根据哪种刺激物引起最大净反应，将总共 70 个味觉反应神经元分为 4 类（36 个蔗糖最佳、19 个 NaCl 最佳、6 个柠檬酸最佳和 9 个 QHCl 最佳）。尽管没有神经元对单磷酸谷氨酸（MPG）或肌苷 5'-单磷酸（IMP）反应最佳，但这两种刺激物的组合在所有蔗糖最佳和一些 NaCl 最佳神经元（n = 43）中引起协同反应（即反应>组成成分反应的 120%）。在 43 个协同神经元中的 41 个中，向蔗糖或 MPG + IMP 中添加 QHCl 会抑制反应（混合物的反应<更有效成分的反应）。表现出 QHCl 抑制的神经元分为两种类型：一种“MS1”型（n = 27），对蔗糖和 MPG + IMP 的反应均被抑制，另一种“MS2”型（n = 14），仅对蔗糖的反应被抑制。没有神经元对 MPG 或 IMP 单独显示抑制反应。MS1 神经元中蔗糖和 MPG + IMP 的抑制比（1-混合物反应/蔗糖或 MPG + IMP 反应）与蔗糖和 MPG + IMP 之间的正相关（r = 0.36）较弱。神经元类型的重建记录位点模式表明在 PbN 中存在化学感受组织。尽管已经证明了 QHCl 抑制的外围基础，但我们的结果表明，在 PbN 中的收敛在塑造味觉混合物的反应中起作用。
