Circuit Mechanisms of Psilocybin Following Chronic Stress

摘要/项目摘要 慢性压力被认为在多种神经精神障碍中起作用。应激相关疾病的标准药物治疗可能需要长达几个月的时间才能产生治疗反应，并可能产生长期的不良偏离目标的效果。单剂量迷幻药物裸盖菇素已被证明在人类和长期应激的啮齿动物中迅速促进长期治疗效果。然而，裸盖菇素在健康和长期应激的大脑中诱导持久变化的神经电路机制仍不清楚。 前额叶皮质(PFC)是受慢性应激影响的重要结构。在患有应激相关障碍的人类中，已经观察到PFC的体积减少、活动不足和功能连接受损。类似地，慢性应激啮齿动物的PFC锥体细胞表现出树突萎缩和兴奋性突触丢失。裸盖菇素通过激活5-羟色胺5-羟色胺受体(5-HT2AR)来增强神经可塑性相关基因的表达。虽然5-HT2AR在包括PFC锥体细胞在内的许多细胞类型的突触后表达，但突触前5-HT2AR也被认为调节到PFC锥体神经元的突触输入。裸盖菇素单次给药可诱导PFC锥体细胞树突状生长并增加树突棘密度。然而，到目前为止，还没有研究检查控制哪些突触(以及相应的树突棘)恢复的规则：裸盖菇素是否是非特异性地增加脊椎和突触的数量，还是优先增强与具有更高5-HT2AR表达的特定输入相对应的棘突和突触？回答这个问题是从机制上理解裸盖菇素如何发挥治疗效果的关键一步。 为了解决这一知识差距，我们将对裸盖菇素对大脑多个区域的影响进行多尺度调查。我们的中心假设是，在慢性应激后受损的PFC的突触输入可以通过裸盖菇素以一种特定的输入方式恢复。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，我们将使用体内和体外的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的影响。这些目标的完成将确定特定的输入规则，控制裸盖菇素诱导受损的前额叶电路的正常化，这对设计更精确、更有效、靶外影响最小的神经精神疗法具有重要意义。

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.