Department of Pharmacology, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico.
Am J Physiol Regul Integr Comp Physiol. 2013 Aug 1;305(3):R252-70. doi: 10.1152/ajpregu.00492.2012. Epub 2013 May 15.
Despite decades of study, it remains a matter of controversy as to whether in rats taste identification is a rapid process that occurs in about 250-600 ms (one to three licks) or a slow process that evolves over seconds. To address this issue, we trained rats to perform a taste-cued two-response discrimination task (2-RDT). It was found that, after learning, regardless of intensity, the delivery of 10 μl of a tastant (e.g., NaCl or monopotassium glutamate, MPG) was sufficient to identify its taste with maximal accuracy within 400 ms. However, despite overtraining, rats rarely stopped licking in one lick. Thus, a one-drop lick reaction task was developed in which subjects had to rapidly stop licking after release of a stop signal (tastants including water) to obtain rewards. The faster they stopped licking, the greater the reward. Rats did not stop licking after receiving either hedonically positive or negative stop signals, and thus failed to maximize rewards even when reinforced with even larger rewards. In fact, the higher the sucrose concentration given as a stop signal, the greater the number of consummatory licks elicited. However, with a stop signal of 2 mM quinine HCl, they stopped licking in ~370 ms, a time faster than that for sucrose or water, thus showing that in this rapid period, quinine HCl evoked an unpalatable response. Indeed, only when rats licked an empty sipper tube would they usually elicit a single lick to obtain a reward (operant licking). In summary, these data indicate that within 400 ms, taste identification and palatability, must either occur simultaneously or with marked overlap.
尽管经过了几十年的研究，但关于大鼠的味觉识别是一个快速过程（约 250-600ms，即一到三次舔舐）还是一个缓慢过程（需要数秒时间），仍然存在争议。为了解决这个问题，我们训练大鼠进行味觉提示双反应辨别任务（2-RDT）。结果发现，无论味觉强度如何，在学习后，只要给予 10μl 的味觉剂（例如 NaCl 或单谷氨酸钾，MPG），大鼠就能在 400ms 内以最大的准确性识别其味道。然而，尽管经过了过度训练，大鼠很少能在一次舔舐中停止。因此，我们开发了一种一滴舔舐反应任务，在此任务中，被试必须在释放停止信号后（包括水在内的味觉剂）快速停止舔舐，以获得奖励。他们停止舔舐的速度越快，奖励就越多。大鼠在接收到愉悦的正性或负性停止信号后都不会停止舔舐，因此即使给予更大的奖励也无法最大化奖励。事实上，给予的蔗糖浓度越高作为停止信号，引发的舔舐次数就越多。然而，当给予 2mM 的奎宁盐酸作为停止信号时，它们在约 370ms 内停止舔舐，这一时间比蔗糖或水更快，表明在这段快速时间内，奎宁盐酸会引起不愉快的反应。事实上，只有当大鼠舔舐空的吮吸管时，它们通常会发出一次舔舐以获得奖励（操作性舔舐）。综上所述，这些数据表明，在 400ms 内，味觉识别和味觉感受性必须同时发生，或者有明显的重叠。
