Role of intercalated amygdala neurons in the extinction of conditioned fear

描述（由申请人提供）：对调节条件恐惧反应获得的回路的研究构成了我们理解人类焦虑症的最大希望。通常用于研究这一过程的模型是经典的恐惧条件反射，其中中性感觉刺激（CS）在与有害刺激配对后获得引起恐惧反应的能力。然而，从临床角度来看，也许更重要的是了解恐惧反应是如何消退的。在实验中，这种灭绝过程是模拟与CS单独的重复介绍，导致条件性恐惧的控制水平下降。这种方法类似于治疗人类恐惧症的方法，即在没有危险的情况下向受试者展示令人恐惧的物体。我们知道，恐惧消失是由杏仁核中的一种新的学习引起的，它与原有的恐惧记忆竞争，以阻止条件性恐惧的表达。然而，这种新的灭绝学习的机制仍然不清楚。这个提议检验了杏仁核的插入（ITC）神经元介导灭绝的假设。已知条件性恐惧的获得涉及到基底外侧杏仁核（BLA）的CS输入的增强。反过来，BLA细胞刺激中央杏仁核（CE）中更多的神经元，这些神经元通过投射到脑干和下丘脑，引起恐惧反应。我们专注于ITC神经元，因为它们可以控制BLA输入对CE神经元的影响，从而控制条件性恐惧的表达。事实上，ITC细胞是GABA能的，它们从BLA接收GABA能输入，并且它们在CE中产生前馈抑制。此外，BLA输入ITC神经元可以经历NMDA依赖性LTP。最后，ITC神经元从边缘下皮层接收大量投射，边缘下皮层被认为在灭绝中起关键作用。这使我们假设，灭绝的结果从NMDA依赖性增强BLA突触传递CS信息ITC神经元，导致CE细胞的BL输入的CS的反应性降低。为了验证这一假设，我们将首先检查灭绝是否与BLA输入到ITC细胞的增强有关，通过比较用补丁方法记录的ITC神经元中的BLA-evoked反应的幅度，该方法记录在从仅经历恐惧条件反射的大鼠与经历恐惧条件反射和灭绝的大鼠获得的切片中。接下来，我们将在恐惧条件反射、灭绝训练和灭绝回忆过程中对ITC细胞进行细胞外记录，并询问ITC神经元是否会像我们的模型预测的那样，由于灭绝训练而对CS变得更加敏感。最后，测试是否ITC细胞介导的边缘下皮层对灭绝的影响，我们将研究细胞外记录ITC神经元的边缘下刺激的反应，并测试是否的性质，潜伏期和诱发反应的持续时间是兼容的想法，ITC神经元产生抑制CE神经元IL刺激。

DESCRIPTION (provided by applicant): Research on the circuits mediating the acquisition of conditioned fear responses constitutes our best hope of understanding human anxiety disorders. The model typically used to study this process is classical fear conditioning where a neutral sensory stimulus (CS) acquires the ability to elicit fear responses after pairing to a noxious stimulus. However, perhaps more important from a clinical perspective is to understand how fear responses subside. Experimentally, this extinction process is modeled with repetitive presentations of the CS alone, resulting in the decline of conditioned fear to control levels. This approach is similar to that used to treat human phobias where subjects are presented with the feared object in the absence of danger. Extinction is known to result from a new learning, which takes place in the amygdala, and competes with the original fear memory to prevent the expression of conditioned fear. However, the mechanisms underlying this new extinction learning remain unclear. This proposal tests the hypothesis that the intercalated (ITC) neurons of the amygdala mediate extinction. The acquisition of conditioned fear is known to involve a potentiation of CS inputs to the basolateral amygdala (BLA). In turn, BLA cells excite more neurons in the central amygdala (CE), which, via their projections to the brainstem and hypothalamus, evoke fear responses. We focus on ITC neurons because they can control the impact of BLA inputs on CE neurons and hence the expression of conditioned fear. Indeed, ITC cells are GABAergic, they receive glutamatergic inputs from BLA, and they generate feed-forward inhibition in CE. Moreover, BLA inputs to ITC neurons can undergo NMDA-dependent LTP. Last, ITC neurons receive a heavy projection from the infralimbic cortex, a cortical area thought to play a critical role in extinction. This leads us to hypothesize that extinction results from an NMDA-dependent potentiation of BLA synapses conveying CS information to ITC neurons, leading to a decreased responsiveness of CE cells to BL inputs about the CS. To test the hypothesis, we will first examine whether extinction is associated with a potentiation of BLA inputs to ITC cells by comparing the amplitude of BLA-evoked responses in ITC neurons recorded with the patch method in slices obtained from rats that underwent fear conditioning only vs. rats that underwent fear conditioning and extinction. Next, we will perform extracellular recordings of ITC cells during fear conditioning, extinction training, and extinction recall, and ask do ITC neurons become more responsive to the CS as a result of extinction training, as predicted by our model. Finally, to test whether ITC cells mediate the influence of the infralimbic cortex on extinction, we will study the responses of extracellularly recorded ITC neurons to infralimbic stimuli and test whether the nature, latency, and duration of evoked responses are compatible with the idea that ITC neurons generate the inhibition of CE neurons by IL stimuli.