Circuit Mechanisms of Psilocybin Following Chronic Stress

摘要/项目总结 慢性压力被认为在多种神经精神疾病中发挥作用。针对应激相关疾病的标准药物治疗可能需要长达数月的时间才能引起治疗反应，并可能产生长期不良的脱靶效应。单剂量的迷幻药裸盖菇素已被证明可以迅速促进人类和慢性应激啮齿动物的长期治疗效果。然而，裸盖菇素在健康和慢性应激大脑中引起持久变化的神经回路机制仍然未知。 前额叶皮层（PFC）是受慢性应激影响的关键结构。在患有压力相关疾病的人中观察到PFC的体积减少、活动减退和功能连接受损。类似地，在慢性应激的啮齿类动物中，PFC锥体细胞表现出树突萎缩和兴奋性突触丢失。裸盖菇素通过涉及5-羟色胺5-HT 2A受体（5-HT 2AR）激活的级联反应增强神经可塑性相关基因的表达。虽然5-HT 2AR在许多细胞类型（包括PFC锥体细胞）中突触后表达，但也已知突触前5-HT 2AR调节PFC锥体神经元的突触输入。裸盖菇素诱导树突生长，并增加树突棘密度PFC锥体细胞后，单剂量。然而，迄今为止还没有研究检查了哪些突触（以及哪些相应的树突棘）被恢复的规则：裸盖菇素是否非特异性地增加棘和突触数量，或者它是否优先增强对应于具有较高5-HT 2AR表达的特定输入的棘和突触？解决这个问题是理解裸盖菇素如何发挥治疗作用的关键一步。 为了解决这一知识差距，我们将对裸盖菇素对多个大脑区域的影响进行多尺度调查。我们的中心假设是，突触输入PFC的慢性应激后受损恢复的输入特定的方式由裸盖菇素。在目标1中，我们将描述裸盖菇素在体内对慢性应激啮齿动物PFC连接和动力学的输入特异性变化的影响。在目标2中，我们将使用体内和离体光遗传学来确定慢性应激和随后的裸盖菇素治疗对输入特异性突触生理学和树突形态学的影响。这些目标的完成将确定管理psilocybin诱导的受损前额叶回路正常化的输入特定规则，对设计更精确和有效的神经精神疗法具有重要意义，并且脱靶效应最小。

ABSTRACT / PROJECT SUMMARY Chronic stress is thought to play a role in multiple neuropsychiatric disorders. Standard pharmacological treatments for stress-related disorders can take up to several months to elicit a therapeutic response and can produce long-term undesirable off-target effects. A single dose of the psychedelic drug psilocybin has been shown to rapidly promote long-lasting therapeutic effects in humans and in chronically stressed rodents. However, the neural circuit mechanisms underlying the lasting changes induced by psilocybin in healthy and chronically stressed brains remain unknown. The prefrontal cortex (PFC) is a key structure impacted by chronic stress. Decreased volume, hypoactivity, and impaired functional connectivity of the PFC has been observed in humans with stress-related disorders. Similarly, PFC pyramidal cells in chronically stressed rodents exhibit dendritic atrophy and excitatory synapse loss. Psilocybin enhances expression of neuroplasticity-related genes through a cascade involving the activation of the serotonin 5-HT2A receptor (5-HT2AR). While the 5-HT2AR is expressed postsynaptically in many cell-types, including PFC pyramidal cells, presynaptic 5-HT2ARs are also known to regulate synaptic input to PFC pyramidal neurons. Psilocybin induces dendritic growth and increases dendritic spine density in PFC pyramidal cells after a single dose. However, no studies to date have examined the rules governing which synapses (and which corresponding dendritic spines) are restored: does psilocybin non-specifically increase spine and synapse number, or does it preferentially enhance spines and synapses corresponding to specific inputs with higher 5-HT2AR expression? Answering this question is a critical step towards a mechanistic understanding of how psilocybin exerts therapeutic effects. To address this gap in knowledge, we will conduct a multiscale investigation of the effects of psilocybin on multiple brain regions. Our central hypothesis is that the synaptic inputs to PFC that are impaired following chronic stress are restored in an input-specific manner by psilocybin. In Aim 1, we will characterize the effects of psilocybin in vivo on input-specific changes in PFC connectivity and dynamics in chronically stressed rodents. In Aim 2, we will use both in vivo and ex vivo optogenetics to determine the effects of chronic stress and subsequent psilocybin treatment on input-specific synaptic physiology and dendritic morphology. The completion of these Aims will identify input-specific rules governing psilocybin-induced normalization of impaired prefrontal circuits, with important implications for the design of even more precise and efficacious neuropsychiatric therapies with minimal off-target effects.