The nucleus accumbens (NAc) plays a crucial role in various mental activities, including positive and negative reinforcement. We previously hypothesized that a balance between dopamine (DA) and adenosine signals regulates the PKA-Rap1 pathway in medium spiny neurons expressing DA D1 receptors (D1R-MSNs) or D2 receptors (D2R-MSNs) and demonstrated that the PKA-Rap1 pathway in D1R-MSNs is responsible for positive reinforcement. Here, we show the role of the PKA-Rap1 pathway in accumbal D2R-MSNs in negative reinforcement. Mice were exposed to electric foot shock as an aversive stimulus. We monitored the phosphorylation level of Rap1gap S563, which leads to the activation of Rap1. Electric foot shocks increased the phosphorylation level of GluN1 S897 and Rap1gap S563 in the NAc. The aversive stimulus-evoked phosphorylation of Rap1gap S563 was detected in accumbal D2R-MSNs and inhibited by pretreatment with adenosine A2a receptor (A2aR) antagonist. A2aR antagonist-treated mice showed impaired aversive memory in passive avoidance tests. AAV-mediated inhibition of PKA, Rap1, or MEK1 in accumbal D2R-MSNs impaired aversive memory in passive avoidance tests, whereas activation of this pathway potentiated aversive memory. Optogenetic inactivation of mesolimbic DAergic neurons induced place aversion in real-time place aversion tests. Aversive response was attenuated by inhibition of PKA-Rap1 signaling in accumbal D2R-MSNs. These results suggested that accumbal D2R-MSNs regulate aversive behaviors through the A2aR-PKA-Rap1-MEK pathway. Our findings provide a novel molecular mechanism for regulating negative reinforcement.

伏隔核 (NAc) 在各种心理活动中起着至关重要的作用，包括正强化和负强化。我们之前假设多巴胺 (DA) 和腺苷信号之间的平衡调节表达 DA D1 受体 (D1R-MSNs) 或 D2 受体 (D2R-MSNs) 的中等多刺神经元中的 PKA-Rap1 通路，并证明 PKA-Rap1 通路在D1R-MSNs 负责正强化。在这里，我们展示了 PKA-Rap1 通路在负强化中累积的 D2R-MSN 中的作用。小鼠暴露于电脚电击作为厌恶刺激。我们监测了导致 Rap1 激活的 Rap1gap S563 的磷酸化水平。电足电击增加了 NAc 中 GluN1 S897 和 Rap1gap S563 的磷酸化水平。Rap1gap S563 的厌恶刺激诱发的磷酸化在累积的 D2R-MSN 中检测到，并被腺苷 A2a 受体 (A2aR) 拮抗剂预处理所抑制。A2aR 拮抗剂治疗的小鼠在被动回避测试中表现出受损的厌恶记忆。AAV 介导的 PKA、Rap1 或 MEK1 在累积 D2R-MSN 中的抑制损害了被动回避测试中的厌恶记忆，而该通路的激活增强了厌恶记忆。在实时位置厌恶测试中，中脑边缘 DAergic 神经元的光遗传学失活诱导了位置厌恶。通过抑制累积 D2R-MSN 中的 PKA-Rap1 信号传导减弱了厌恶反应。这些结果表明，accumbal D2R-MSNs 通过 A2aR-PKA-Rap1-MEK 通路调节厌恶行为。我们的发现为调节负强化提供了一种新的分子机制。