Ketamine is a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist with antidepressant, anxiolytic, and memory effects in clinical and preclinical studies. The present studies investigated the behavioral effects of ketamine in animals exposed to a consummatory successive negative contrast (cSNC) task involving unexpected reward downshift, negative emotion (frustration), and aversive memory. Food-restricted male rats had 5-min access to 32 % sucrose in each of 10 preshift sessions followed by 4 % sucrose in 4 postshift sessions. Unshifted controls had access to 4 % sucrose during all 14 sessions. Ketamine (10 mg/kg, ip) was injected 30 min before sessions 11 and 12 (Experiment 1) or immediately after session 11 (Experiment 3). The results showed that both pre- and postdownshift session injection of ketamine increased consummatory suppression, as Group 32-4/Ket exhibited lower sucrose intake than Groups 32-4/Sal, 4-4/Ket, and 4-4/Sal. These effects extended beyond the day(s) of injection. Experiments 2 and 4 showed that the same dose, route of administration, and time of injection induced significant conditioned taste aversion to 4 % sucrose, in the absence of reward downshift. These data suggest that ketamine induces an aversive state that may summate with frustration induced by reward downshift in the cSNC task and also support a conditioned taste aversion to 4 % sucrose in the absence of reward downshift. Implications for these and other experiments involving pre- and postsession administration of ketamine are discussed.

氯胺酮是一种非竞争性N-甲基-d-天冬氨酸(NMDA) 受体拮抗剂，在临床和临床前研究中具有抗抑郁、抗焦虑和记忆作用。目前的研究调查了氯胺酮对接受完成性连续负对比（cSNC）任务的动物的行为影响，其中包括意外的奖励下降、消极情绪（沮丧）和厌恶记忆。限食的雄性大鼠在 10 次轮班前的每次 5 分钟内摄入 32% 的蔗糖，随后在 4 次轮班后的时段中摄入 4% 的蔗糖。未转移的对照在所有 14 个疗程中都可以摄入 4% 的蔗糖。在第 11 节和第 12 节（实验 1）之前 30 分钟或在第 11 节（实验 3）之后立即注射氯胺酮（10 mg/kg，ip）。结果表明，降班前和降班后注射氯胺酮均增加了完成性抑制，因为组 32-4/Ket 表现出比组 32-4/Sal、4-4/Ket 和 4-4/Sal 更低的蔗糖摄入量。这些影响持续到注射后。实验2和4表明，在没有奖赏下调的情况下，相同的剂量、给药途径和注射时间诱导了对4%蔗糖的显着条件性味觉厌恶。这些数据表明，氯胺酮会诱发一种厌恶状态，这种状态可能会导致 cSNC 任务中奖励下调所引起的挫败感，并且还支持在没有奖励下调的情况下对 4% 蔗糖的条件性味觉厌恶。讨论了这些实验和其他涉及治疗前和治疗后服用氯胺酮的实验的意义。