Pritchard T C, Scott T R
Brain Res. 1982 Dec 16;253(1-2):81-92. doi: 10.1016/0006-8993(82)90675-8.
The physiological importance of L-amino acids implies that the gustatory system should be sensitive to their presence in the environment. This notion is reinforced by research showing that rats are able to self-regulate their dietary consumption of amino acids and other important nutrients. This paper describes two studies which begin a systematic evaluation of the neural and behavioral effects of L-amino acids on gustation in the rat. The first experiment defined the neural thresholds, intensity-response functions and time courses of whole chorda tympani nerve responses to 12 stimuli. Thresholds varied from 10(-4) M (arginine) to 8 X 10(-2) M (proline), with pH-related amino acids being low and those reported by humans to be sweet being high. Maximum neural effectiveness, relative to the resting level of neural activity, ranged from 108% (2.0 M lysine-hydrochloride) to 8% (0.1 M leucine), with pH-related stimuli evoking the greatest activity. Neural time courses were varied, and often did not include well-defined phasic and tonic components. The second experiment measured the rat's preferences in 24-h two-bottle tests. Preference thresholds were typically lower than neural thresholds, presumably due to extra-chorda tympani input involved in the perception of flavor. They ranged from 2 X 10(-6) M (methionine) to 6 X 10(-2) m (leucine) and were in good agreement with psychophysically defined humar thresholds. Seven stimuli were preferred at low concentrations, but only two (alanine, leucine) continued to be appetitive as intensity increased. Preferences were predictable for 10 of the 12 stimuli from psychophysical reports. Rats also rejected amino acids in direct proportion to their toxicity, demonstrating the protective function of the taste-hedonic system.
L-氨基酸的生理重要性表明味觉系统应对环境中L-氨基酸的存在敏感。有研究表明大鼠能够自我调节其饮食中氨基酸和其他重要营养素的摄入量，这一观点得到了进一步强化。本文描述了两项研究，它们开始对L-氨基酸对大鼠味觉的神经和行为影响进行系统评估。第一个实验确定了鼓索神经对12种刺激的神经阈值、强度-反应函数和时间进程。阈值范围从10^(-4)M（精氨酸）到8×10^(-2)M（脯氨酸），与pH相关的氨基酸阈值较低，而人类报告为甜的氨基酸阈值较高。相对于神经活动的静息水平，最大神经效应范围从108%（2.0M盐酸赖氨酸）到8%（0.1M亮氨酸），与pH相关的刺激引发的活动最大。神经时间进程各不相同，通常不包括明确的相位和紧张成分。第二个实验在24小时双瓶测试中测量了大鼠的偏好。偏好阈值通常低于神经阈值，可能是由于味觉感知中涉及鼓索神经以外的输入。它们的范围从2×10^(-6)M（蛋氨酸）到6×10^(-2)M（亮氨酸），与心理物理学定义的人类阈值高度一致。七种刺激在低浓度下受到偏好，但随着强度增加，只有两种（丙氨酸、亮氨酸）仍然具有吸引力。根据心理物理学报告，12种刺激中有10种的偏好是可预测的。大鼠也会根据氨基酸的毒性成比例地拒绝它们，这证明了味觉-享乐系统的保护功能。
