Excessive serotonin (5-HT) signaling plays a critical role in the etiology of alcohol use disorder. The central nucleus of the amygdala (CeA) is a key player in alcohol-dependence associated behaviors. The CeA receives dense innervation from the dorsal raphe nucleus, the major source of 5-HT, and expresses 5-HT receptor subtypes (e.g., 5-HT2C and 5-HT1A) critically linked to alcohol use disorder. Notably, the role of 5-HT regulating rat CeA activity in alcohol dependence is poorly investigated. Here, we examined neuroadaptations of CeA 5-HT signaling in adult, male Sprague Dawley rats using an established model of alcohol dependence (chronic intermittent alcohol vapor exposure), ex vivo slice electrophysiology and ISH. 5-HT increased frequency of sIPSCs without affecting postsynaptic measures, suggesting increased CeA GABA release in naive rats. In dependent rats, this 5-HT-induced increase of GABA release was attenuated, suggesting blunted CeA 5-HT sensitivity, which partially recovered in protracted withdrawal (2 weeks). 5-HT increased vesicular GABA release in naive and dependent rats but had split effects (increase and decrease) after protracted withdrawal indicative of neuroadaptations of presynaptic 5-HT receptors. Accordingly, 5-HT abolished spontaneous neuronal firing in naive and dependent rats but had bidirectional effects in withdrawn. Alcohol dependence and protracted withdrawal did not alter either 5-HT1A-mediated decrease of CeA GABA release or Htr1a expression but disrupted 5-HT2C-signaling without affecting Htr2c expression. Collectively, our study provides detailed insights into modulation of CeA activity by the 5-HT system and unravels the vulnerability of the CeA 5-HT system to chronic alcohol and protracted withdrawal.

SIGNIFICANCE STATEMENT Elevated GABA signaling in the central nucleus of the amygdala (CeA) underlies key behaviors associated with alcohol dependence. The CeA is reciprocally connected with the dorsal raphe nucleus, the main source of serotonin (5-HT) in the mammalian brain, and excessive 5-HT signaling is critically implicated in the etiology of alcohol use disorder. Our study, using a well-established rat model of alcohol dependence, ex vivo electrophysiology and ISH, provides mechanistic insights into how both chronic alcohol exposure and protracted withdrawal dysregulate 5-HT signaling in the CeA. Thus, our study further expands our understanding of CeA cellular mechanisms involved in the pathophysiology of alcohol dependence and withdrawal.

过量的5-羟色胺（5-HT）信号在酒精使用障碍的病因中起着至关重要的作用。杏仁核（CeA）的中枢核是酒精依赖相关行为的关键参与者。CeA从背缝核（5-HT的主要来源）接受密集的神经支配，并表达与酒精使用障碍严重相关的5-HT受体亚型（例如5-HT2C和5-HT1A）。值得注意的是，5-HT调节大鼠CeA活性在酒精依赖中的作用研究很少。在这里，我们使用建立的酒精依赖模型（慢性间歇性酒精蒸气暴露）离体检查成年雄性Sprague Dawley大鼠的CeA 5-HT信号传导的神经适应性切片电生理学和ISH。5-HT增加sIPSC的频率而不影响突触后的措施，这表明幼稚大鼠中CeA GABA的释放增加。在成年大鼠中，这种5-HT诱导的GABA释放增加被减弱，表明CeA 5-HT敏感性减弱，在长期停药（2周）后部分恢复。5-HT增加了幼稚和依赖大鼠的囊泡GABA释放，但在长期停药后有分裂效应（增加和减少），表明突触前5-HT受体的神经适应。因此，5-HT消除了幼稚和依赖大鼠的自发神经元放电，但在撤回时具有双向作用。酒精依赖和长期停药不会改变5-HT1A介导的CeA GABA释放或Htr1a减少表达但在不影响Htr2c表达的情况下破坏了5-HT2C信号。总的来说，我们的研究提供了对5-HT系统对CeA活性调节的详细见解，并揭示了CeA 5-HT系统对慢性酒精和长期停药的脆弱性。

意义声明杏仁核（CeA）中央核中GABA信号的升高是与酒精依赖相关的关键行为的基础。CeA与哺乳动物脑中5-羟色胺（5-HT）的主要来源背沟核相互连接，并且过量的5-HT信号传导与酒精使用障碍的病因密切相关。我们的研究使用已建立的酒精依赖，离体电生理学和ISH大鼠模型，提供了有关慢性酒精暴露和长期停药如何在CeA中失调5-HT信号的机制的见解。因此，我们的研究进一步扩展了我们对涉及酒精依赖和戒断的病理生理学的CeA细胞机制的理解。