Converging clinical and preclinical evidence demonstrates that depressive phenotypes are associated with synaptic dysfunction and dendritic simplification in cortico-limbic glutamatergic areas. On the other hand, the rapid antidepressant effect of acute ketamine is consistently reported to occur together with the rescue of dendritic atrophy and reduction of spine number induced by chronic stress in the hippocampus and prefrontal cortex of animal models of depression. Nevertheless, the molecular mechanisms underlying these morphological alterations remain largely unknown.

Here, we found that miR-9-5p levels were selectively reduced in the hippocampus of rats vulnerable to Chronic Mild Stress (CMS), while acute subanesthetic ketamine restored its levels to basal condition in just 24h; miR-9-5p expression inversely correlated with the anhedonic phenotype. A decrease of miR-9-5p was reproduced in an in vitro model of stress, based on primary hippocampal neurons incubated with the stress hormone corticosterone. In both CMS animals and primary neurons, decreased miR-9-5p levels were associated with dendritic simplification, while treatment with ketamine completely rescued the changes.

In vitro modulation of miR-9-5p expression showed a direct role of miR-9-5p in regulating dendritic length and spine density in mature primary hippocampal neurons. Among the putative target genes tested, Rest and Sirt1 were validated as biological targets in primary neuronal cultures. Moreover, in line with miR-9-5p changes, REST protein expression levels were remarkably increased in both CMS vulnerable animals and corticosterone-treated neurons, while ketamine completely abolished this alteration. Finally, the shortening of dendritic length in corticosterone-treated neurons was shown to be partly rescued by miR-9-5p overexpression and dependent on REST protein expression.

Overall, our data unveiled the functional role of miR-9-5p in the remodeling of dendritic arbor induced by stress/corticosterone in vulnerable animals and its rescue by acute antidepressant treatment with ketamine.

临床和临床前证据的融合表明，抑郁表型与皮质边缘谷氨酸能区域的突触功能障碍和树突简化有关。另一方面，据报道，急性氯胺酮的快速抗抑郁作用与抑郁症动物模型的海马和前额叶皮层慢性应激引起的树突萎缩和脊柱数量减少一起发生。然而，这些形态学改变背后的分子机制在很大程度上仍然未知。

在这里，我们发现 miR-9-5p 水平在易受慢性轻度压力​​ (CMS) 影响的大鼠海马中选择性降低，而急性亚麻醉剂氯胺酮仅在 24 小时内将其水平恢复到基础状态；miR-9-5p 表达与快感缺失表型呈负相关。基于与应激激素皮质酮一起孵育的原代海马神经元，在体外应激模型中再现了 miR-9-5p 的减少。在 CMS 动物和原代神经元中，降低的 miR-9-5p 水平与树突简化有关，而氯胺酮治疗完全挽救了这些变化。

miR-9-5p 表达的体外调节表明 miR-9-5p 在调节成熟原代海马神经元的树突长度和棘密度中具有直接作用。在测试的假定靶基因中，Rest 和 Sirt1 被验证为原代神经元培养物中的生物靶标。此外，与 miR-9-5p 的变化一致，CMS 脆弱动物和皮质酮处理的神经元的 REST 蛋白表达水平显着增加，而氯胺酮完全消除了这种改变。最后，皮质酮处理的神经元中树突长度的缩短显示部分通过 miR-9-5p 过表达并依赖于 REST 蛋白表达来挽救。

总体而言，我们的数据揭示了 miR-9-5p 在脆弱动物应激/皮质酮诱导的树突状乔木重塑中的功能作用，以及通过氯胺酮急性抗抑郁治疗的拯救。