Yu W Z, Sclafani A, Delamater A R, Bodnar R J
Neuropsychology, Queens College, City University of New York, Flushing 11367, USA.
Pharmacol Biochem Behav. 1999 Nov;64(3):573-84. doi: 10.1016/s0091-3057(99)00124-0.
Relatively little is known about the neurochemical and pharmacological mechanisms involved in flavor preference learning. The present study examined the ability of the opioid antagonist, naltrexone to alter the acquisition and expression of flavor preferences conditioned by the sweet taste of sucrose. This was accomplished by adding a novel flavor (the CS+) to a sucrose solution, and a different flavor (the CS-) to a less-preferred saccharin solution. Rats were trained to drink these solutions with an open gastric fistula (sham-feeding), which minimized postingestive actions. Food-restricted (Experiments 1 and 2A) and ad lib-fed (Experiment 2B) rats were given either limited (Experiment 1) or unlimited (Experiment 2) access to the CS+ and CS- solutions during one-bottle training. Preferences were assessed in two-bottle tests (with the CS+ and CS- flavors presented in mixed sucrose-saccharin solutions) following vehicle or naltrexone (0.1-10 mg/kg, SC) treatment. The rats displayed significant CS+ preferences following vehicle, particularly after unlimited access training. In four of five experiments, naltrexone significantly reduced total intakes during the two-bottle, sham-feeding tests. Except for one instance, however, the drug failed to block the preference for the CS+ flavor over the CS- flavor. The effects of naltrexone (0.1 mg/kg) on the acquisition of flavor preferences were studied in sham-feeding rats under limited (Experiment 3A) and unlimited (Experiment 3B) training access conditions. Rats treated with naltrexone during training displayed similar CS+ preferences as did saline-treated rats, even though they consumed less CS+ during training. The naltrexone-trained rats also displayed smaller reductions in total or CS+ intakes than did saline-trained rats when all rats were treated with a 2.5 mg/kg dose of naltrexone during testing. As in previous studies, these results show that naltrexone significantly reduces the intake of sweet solutions, yet it has little or no effect on the acquisition or expression of flavor preferences conditioned by sucrose in sham-feeding rats.
关于味觉偏好学习所涉及的神经化学和药理机制，人们了解得相对较少。本研究考察了阿片类拮抗剂纳曲酮改变由蔗糖甜味所引发的味觉偏好习得和表达的能力。这是通过在蔗糖溶液中添加一种新口味（条件刺激物 CS+），并在较不喜欢的糖精溶液中添加另一种不同口味（条件刺激物 CS-）来实现的。采用开放式胃瘘（假饲）训练大鼠饮用这些溶液，从而将摄食后的影响降至最低。在单瓶训练期间，对限食（实验 1 和 2A）和自由进食（实验 2B）的大鼠给予有限（实验 1）或无限（实验 2）量的 CS+和 CS-溶液。在给予溶剂或纳曲酮（0.1 - 10 毫克/千克，皮下注射）处理后，通过双瓶测试（将 CS+和 CS-口味呈现在混合的蔗糖 - 糖精溶液中）评估偏好。给予溶剂后，大鼠表现出显著的 CS+偏好，尤其是在无限量摄入训练后。在五个实验中的四个实验中，纳曲酮在双瓶假饲测试期间显著降低了总摄入量。然而，除了一个实例外，该药物未能阻断对 CS+口味相对于 CS-口味的偏好。在限食（实验 3A）和无限量摄入训练（实验 3B）条件下，研究了纳曲酮（0.1 毫克/千克）对假饲大鼠味觉偏好习得的影响。训练期间用纳曲酮处理的大鼠表现出与用生理盐水处理的大鼠相似的 CS+偏好，尽管它们在训练期间摄入的 CS+较少。当在测试期间所有大鼠都接受 2.5 毫克/千克剂量的纳曲酮处理时，用纳曲酮训练的大鼠在总摄入量或 CS+摄入量方面的减少也比用生理盐水训练的大鼠小。与先前的研究一样，这些结果表明，纳曲酮显著降低了甜味溶液的摄入量，但对假饲大鼠中由蔗糖引发的味觉偏好的习得或表达几乎没有影响。
