Roll J M, McSweeney F K, Meil W M, Hinson J M, See R E
University of Vermont, Human Behavioral Pharmacology Laboratory, Department of Psychiatry, 38 Fletcher Place, Ira Allen School, Burlington, VT 05401-1419, USA.
Washington State University, Department of Psychology, Pullman, WA 99164-4820, USA.
Behav Processes. 1996 Aug;37(1):9-20. doi: 10.1016/0376-6357(95)00068-2.
Two experiments examined within-session changes in operant responding when cocaine or cocaine plus food served as the reinforcer. In Experiment 1, male rats self-administered intravenous cocaine according to several fixed interval schedules. The within-session patterns of responding differed for the different schedules early in the session, but they converged by 50 minutes into the session. Because this convergence occurred regardless of the amount of cocaine consumed, it questions the response-stereotypy and dopamine-loading explanations for within-session changes in responding for cocaine reinforcers. In Experiment 2, rats responded for sweetened condensed milk during baseline sessions. During experimental sessions, responding produced cocaine in addition to the condensed milk. The addition of cocaine altered the pattern of responding during the early (first 15 minutes), but not the later (last 45 minutes), parts of the session. These results suggest that different factors produce the early-session increases and late-session decreases in responding. They are also consistent with the idea that the early-session changes in responding represent changes in'arousal'.
两项实验研究了以可卡因或可卡因加食物作为强化物时，操作性反应在实验过程中的变化。在实验1中，雄性大鼠根据几种固定间隔时间表自行静脉注射可卡因。在实验初期，不同时间表的反应模式有所不同，但到实验进行50分钟时，它们趋于一致。由于这种趋同现象的发生与可卡因的摄入量无关，这对可卡因强化物反应的实验过程中变化的反应刻板性和多巴胺负荷解释提出了质疑。在实验2中，大鼠在基线期对甜炼乳做出反应。在实验期，反应除了能得到炼乳外，还能得到可卡因。可卡因的添加改变了实验前期（前15分钟）的反应模式，但没有改变后期（最后45分钟）的反应模式。这些结果表明，不同因素导致了实验前期反应增加和后期反应减少。它们也与实验前期反应变化代表“唤醒”变化的观点一致。
