Rosen Andrew M, Roussin Andre T, Di Lorenzo Patricia M
Department of Psychology, Binghamton University Binghamton, NY, USA.
Front Neurosci. 2010 Oct 15;4:175. doi: 10.3389/fnins.2010.00175. eCollection 2010.
To qualify as a "basic" taste quality or modality, defined as a group of chemicals that taste alike, three empirical benchmarks have commonly been used. The first is that a candidate group of tastants must have a dedicated transduction mechanism in the peripheral nervous system. The second is that the tastants evoke physiological responses in dedicated afferent taste nerves innervating the oropharyngeal cavity. Last, the taste stimuli evoke activity in central gustatory neurons, some of which may respond only to that group of tastants. Here we argue that water may also be an independent taste modality. This argument is based on the identification of a water dedicated transduction mechanism in the peripheral nervous system, water responsive fibers of the peripheral taste nerves and the observation of water responsive neurons in all gustatory regions within the central nervous system. We have described electrophysiological responses from single neurons in nucleus of the solitary tract (NTS) and parabrachial nucleus of the pons, respectively the first two central relay nuclei in the rodent brainstem, to water presented as a taste stimulus in anesthetized rats. Responses to water were in some cases as robust as responses to other taste qualities and sometimes occurred in the absence of responses to other tastants. Both excitatory and inhibitory responses were observed. Also, the temporal features of the water response resembled those of other taste responses. We argue that water may constitute an independent taste modality that is processed by dedicated neural channels at all levels of the gustatory neuraxis. Water-dedicated neurons in the brainstem may constitute key elements in the regulatory system for fluid in the body, i.e., thirst, and as part of the swallowing reflex circuitry.
要成为一种“基本”味觉品质或味觉模式（定义为一组味道相似的化学物质），通常使用三个实证基准。第一个是，一组候选味觉物质必须在外周神经系统中有专门的转导机制。第二个是，这些味觉物质在支配口咽腔的专门传入味觉神经中引发生理反应。最后，味觉刺激在中枢味觉神经元中引发活动，其中一些神经元可能仅对该组味觉物质做出反应。在此，我们认为水也可能是一种独立的味觉模式。这一观点基于在外周神经系统中发现了一种专门用于水的转导机制、外周味觉神经中对水有反应的纤维，以及在中枢神经系统内所有味觉区域中观察到对水有反应的神经元。我们已经描述了在麻醉大鼠中，作为味觉刺激呈现的水分别对孤束核（NTS）和脑桥臂旁核（啮齿动物脑干中的前两个中枢中继核）中单个神经元的电生理反应。对水的反应在某些情况下与对其他味觉品质的反应一样强烈，有时在对其他味觉物质无反应的情况下也会出现。观察到了兴奋性和抑制性反应。此外，对水的反应的时间特征与其他味觉反应相似。我们认为水可能构成一种独立的味觉模式，在味觉神经轴的各个层面都由专门的神经通道进行处理。脑干中专门对水有反应的神经元可能构成体内液体调节系统（即口渴）的关键要素，也是吞咽反射回路的一部分。
