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

 描述(申请人提供)：以前的研究提供了重要的实验证据，证明垂体腺苷酸环化酶激活多肽(PACAP)介导的信号在调节实验动物和人类受试者的焦虑中所起的作用。已经证明，PACAP可能通过其在杏仁核和BNST两个相互作用的大脑区域的作用来调节焦虑相关的行为。然而，PACAP介导的脑内效应的突触和网络机制还知之甚少。在这里，我们提出了一项行为和电生理相结合的研究，以解决关于PACAP诱导的BLA-BNST回路中突触和网络水平的改变的性质的具体问题，这可能有助于控制焦虑状态。在目标1中，我们将探讨PACAP在BLA向两个BNST亚群ovBNST和adBNST的投射中对突触和神经元功能的调节作用。ovBNST和adBNST对焦虑的调节是相反的--激活ovBNST可以引起焦虑，而激活adBNST可以缓解焦虑。我们将在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(ChR2)，并在BNST的两个亚区的神经元上光刺激相应的突触纤维。我们的初步发现表明，PACAP选择性地在ovBNST中表达，并在ovBNST的输入端增强兴奋性突触反应，但在adBNST的输入端不增强兴奋性突触反应。我们推测，神经肽PACAP可能通过不同地影响BLA投射到不同BNST亚区的突触效率，从而改变BLA-ovBNST-adBNST环路中的信号流，从而抑制adBNST，从而参与焦虑状态的调节。这将解释BNST中PACAP引发焦虑的能力，因为adBNST的直接光遗传抑制被证明是导致焦虑的。在目标2中，我们将验证一种假说，即臂旁核(PBN)和下丘脑室旁核(PVN)可能是BNST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，利用活体光遗传学，我们将探索PBN-BNST和PVN-BNST投射在焦虑状态调节中发挥作用的可能性，可能是通过在焦虑性条件下OVBNST释放PACAP来实现的。以这些考虑为基础，我们的首要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大脑回路的相互作用组件的水平上调节焦虑。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讯失调，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.