Instrumental actions are initially goal-directed and driven by their associated outcome. However, with repeated experience habitual actions develop which are automated and efficient, as they are instead driven by antecedent stimuli. Dopamine is thought to facilitate the transition from goal-directed to habitual actions. This idea has been largely derived from evidence that psychostimulants accelerate the development of habitual actions. In the current study, we examined the impact of L-dopa (levodopa or L-dihydroxyphenylalanine), which also potentiates dopamine activity, on habitual learning. L-dopa was systemically administered prior to training rats to press a lever for a food outcome. When tested, L-dopa exposed animals were insensitive to changes in the value of the food outcome, and hence demonstrated accelerated habitual behavioral control compared to control animals that remained goal directed. We also showed that when N-acetylcysteine (NAC), an antioxidant and regulator of glutamate activity, was co-administered with L-dopa, it prevented the transition to habitual behavior; an effect demonstrated previously for cocaine. Therefore, this study establishes similarities between L-dopa and psychostimulants in both the development and prevention of habitual actions, and supports the notion that excess dopamine potentiates habitual learning. This finding extends the limited existing knowledge of the impact of L-dopa on learning and behavior, and has implications for neurological disorders where L-dopa is the primary treatment.

工具性行动最初是目标导向的，并由其相关结果驱动。然而，随着重复的经验，习惯性的行为会发展起来，这些行为是自动化的和有效的，因为它们是由先前的刺激驱动的。多巴胺被认为有助于从目标导向到习惯性行为的转变。这个想法很大程度上源于精神兴奋剂加速习惯性行为发展的证据。在目前的研究中，我们检查了 L-多巴（左旋多巴或 L-二羟基苯丙氨酸）对习惯性学习的影响，它也增强了多巴胺的活性。在训练大鼠按压杠杆以获得食物结果之前，系统地施用左旋多巴。在测试时，暴露于左旋多巴的动物对食物结果价值的变化不敏感，并因此与保持目标导向的对照动物相比，表现出加速的习惯性行为控制。我们还表明，当N-乙酰半胱氨酸 (NAC) 是一种抗氧化剂和谷氨酸活性调节剂，与左旋多巴共同给药，可防止向习惯行为转变；先前对可卡因证明的效果。因此，本研究确立了左旋多巴和精神兴奋剂在习惯性行为的发展和预防方面的相似性，并支持过量多巴胺增强习惯性学习的观点。这一发现扩展了关于左旋多巴对学习和行为影响的有限现有知识，并对左旋多巴作为主要治疗方法的神经系统疾病产生了影响。