PACAP-mediated modulation of amygdalar-BNST interactions: implications for control of anxiety states

 描述（由申请人提供）：先前的研究为垂体腺苷酸环化酶激活多肽（PACAP）介导的信号传导在实验动物和人类受试者的焦虑调节中的作用提供了重要的实验证据。已经证明，PACAP可以通过其在两个相互作用的大脑区域（杏仁核和BNST）中的作用来调节焦虑相关行为。然而，突触和网络机制的PACAP介导的影响，在大脑中知之甚少。在这里，我们提出了一个相结合的行为和电生理研究，以解决特定的问题，PACAP诱导的突触和网络水平的修改BLA-BNST电路的性质，可能有助于控制焦虑状态。在目的1中，我们将探索PACAP在调节从BLA到两个BNST亚类（ovBNST和adBNST）的投射中的突触和神经元功能中的作用，已知这两个亚类以相反的方向调节焦虑-ovBNST的激活被证明会诱导焦虑，而adBNST的激活是抗焦虑的。我们将在BLA神经元中的神经元特异性启动子CaMKIIα的控制下表达光敏蛋白-通道视紫红质-2（ChR 2），并光刺激BNST两个亚部中神经元上的相应纤维突触。由于我们的初步研究结果表明，PACAP选择性地在ovBNST中表达，并在ovBNST的输入处而不是在adBNST的输入处增强兴奋性突触反应，因此我们假设神经肽PACAP可能通过差异性地影响BLA投射到不同BNST亚部的突触功效而有助于焦虑状态的调节，因此，以禁止adBNST的方式修改BLA-ovBNST-adBNST电路中的信号流。这将解释PACAP在BNST中触发焦虑的能力，因为adBNST的直接光遗传学抑制被证明是致焦虑的。目的2：我们将验证一个假设，即臂旁核（PBn）和室旁核（PVN）可能是BNST中内源性PACAP的来源，有助于调节焦虑，因为PBn和PVN都具有PACAP能神经元并投射到BNST。因此，使用体内光遗传学，我们将探索PBn-BNST和PVN-BNST投射在焦虑状态调节中发挥功能作用的可能性，可能是通过在致焦虑条件下ovBNST中释放PACAP。以这些考虑为基础，我们的总体目标是定义突触和神经网络机制，这些机制可能有助于在相应脑回路的相互作用组件水平上调节焦虑。这些问题很重要，因为焦虑症可能反映了控制先天恐惧反应的神经回路组件之间的通信失调，包括杏仁核和BNST。

 DESCRIPTION (provided by applicant): Previous studies provide significant experimental evidence for the role of pituitary adenylate cyclase-activating polypeptide (PACAP)-mediated signaling in regulation of anxiety in both experimental animals and human subjects. It has been demonstrated that PACAP may regulate anxiety-related behavior through its actions in two interacting brain regions, the amygdala and BNST. However, synaptic and network mechanisms of PACAP-mediated effects in the brain are poorly understood. Here, we propose a combined behavioral and electrophysiological study in order to address specific questions about the nature of PACAP-induced synaptic and network-level modifications in BLA-BNST circuits, possibly contributing to control of anxiety states. In Aim 1, we will explore the role of PACAP in regulation of synaptic and neuronal functions in projections from the BLA to two BNST subdivisions, ovBNST and adBNST, known to regulate anxiety in opposite directions- activation of ovBNST was shown to induce anxiety, whereas activation of adBNST is anxiolytic. We will express the photosensitive protein, channelrhodopsin-2 (ChR2), under control of the neuron-specific promoter CaMKIIα in BLA neurons and photostimulate corresponding fibers synapsing on neurons in both BNST subdivisions. As our preliminary findings indicate that PACAP is selectively expressed in ovBNST and potentiates excitatory synaptic responses at inputs to ovBNST but not at inputs to adBNST, we hypothesize that neuropeptide PACAP may contribute to regulation of anxiety states by differentially affecting synaptic efficacy at BLA projections to different BNST subdivisions, and, therefore, modifying the signal flow in BLA- ovBNST-adBNST circuits in such a way that adBNST is inhibited. This would explain the ability of PACAP in BNST to trigger anxiety, as direct optogenetic inhibition of adBNST was shown to be anxiogenic. In Aim 2, we will test a hypothesis that the parabrachial nucleus (PBn) and paraventricular nucleus of the hypothalamus (PVN) might be the sources of endogenous PACAP in BNST, contributing to regulation of anxiety, as both PBn and PVN possess PACAPergic neurons and project to BNST. Thus, using in vivo optogenetics, we will explore the possibility that PBn-BNST and PVN-BNST projections play a functional role in regulation of anxiety states, possibly through the release of PACAP in ovBNST under anxiogenic conditions. With these considerations as a foundation, our overarching goal is to define synaptic and neural network mechanisms which may contribute to regulation of anxiety at the level of interacting components of corresponding brain circuits. These questions are important because anxiety disorders may reflect dysregulation of communication between components of the neural circuits controlling innate fear responses, including the amygdala and BNST.