杏仁核：功能与神经基础

文献信息

中文摘要

本综述总结了目前对杏仁核的认识。作为边缘系统的重要组成部分，杏仁核对环境刺激（如声音）高度敏感。尽管杏仁核神经元对声音的反应通常不如初级听皮层神经元那样强烈，但这些神经元的最低反应阈值与行为听力图一致。当通过感觉信息处理检测到威胁时，会立即触发战斗或逃跑反应，如僵直和心率加快。通过学习和记忆环境事件（尤其是可能造成伤害的事件）及其对各种本能行为（如性冲动和母性行为）以及情绪表达（如恐惧和攻击）的影响，它在物种的生存和延续中起着至关重要的作用。杏仁核神经元对环境声音的反应通常由早期尖锐反应成分和晚期缓慢反应成分组成。早期反应负责对有意义的信息（如危险的存在）进行快速处理，而晚期反应可能与情绪处理有关。事实上，当存在捕食者线索或处于恐惧条件化过程中时，杏仁核的早期反应会增强。具有不同情绪色调的声音可以在杏仁核中触发不同的反应模式。大量文献表明，杏仁核在巴甫洛夫恐惧条件化中起着至关重要的作用。在此过程中，条件刺激（CS）和非条件刺激（US）都汇聚到外侧杏仁核（LA）的神经元上，从而激活中央杏仁核（CeA）并触发条件反应。有趣的是，杏仁核可与多种精神疾病相关，如焦虑障碍、抑郁，甚至耳鸣。杏仁核由LA、基底外侧杏仁核（BLA）、基底内侧杏仁核（BMA）、CeA、内侧杏仁核（MeA）和皮质杏仁核（CoA）组成。外侧杏仁核复合体（LA、BLA和BMA）主要由谷氨酸能锥体神经元（PNs，占总神经元的70%-85%）组成，而CeA主要包含GABA能神经元（>90%的神经元）。谷氨酸和GABA是杏仁核中的两种主要神经递质。此外，杏仁核的神经活动还可受到来自大脑其他区域的各种神经递质、神经调质和激素的调节，如乙酰胆碱（ACh）、多巴胺（DA）、5-羟色胺（5-HT）、去甲肾上腺素（NE）和糖皮质激素。LA从丘脑（快速低通路）和皮层（缓慢高通路）接收感觉信息。LA中的PNs可直接兴奋CeA中的投射神经元，从而触发相应的行为反应，如紧急反应或恐惧条件化。LA的PNs还可投射到BLA和BMA进行进一步的信息处理。BLA/BMA中的PNs可直接投射到CeA，或投射到海马和前额叶皮层进行处理。快速的恐惧条件化可通过快速低通路实现。然而，通过缓慢高通路的信息处理结果可能调节或覆盖通过快速低通路的初始恐惧反应。CeA中超过90%的神经元是抑制性神经元，抑制脑干的神经活动。例如，在僵直行为的背景下，它们可以抑制前包钦格复合体的神经活动，从而抑制呼吸。CeA还包含兴奋性神经元（<10%）。它们可以兴奋下丘脑或尾侧脑桥网状核中的神经元，触发战斗或逃跑反应或导致听觉惊跳反应增强。

英文摘要

This review summarizes our current understanding of the amygdala. As an important part of the limbic system, the amygdala is highly sensitive to environmental stimuli such as sounds. Although the responses of amygdala neurons to sounds are usually not as robust as those of neurons in the primary auditory cortex, the lowest response thresholds of these neurons are consistent with the behavioral audiogram. When a threat is detected through sensory information processing, it immediately triggers a fight-or-flight response, such as freezing and heart rate increase. By learning and remembering environmental events (especially those that may cause harm) and its effects on various instinctive behaviors (such as sexual impulse and maternal behaviors) as well as emotional expressions (such as fear and aggression), it plays a crucial role in the survival and continuation of the species. The response of amygdala neurons to environmental sounds is often composed of an early sharp response component and a late slow response component. The early response is responsible for rapid processing of meaningful information (such as the presence of danger), while the late response can be related to emotional processing. Indeed, the early response of the amygdala is enhanced when there are predator cues or during fear conditioning. Sounds with different emotional tones can trigger different response patterns in the amygdala. It is well documented that the amygdala plays a crucial role in Pavlovian fear conditioning. During this process, both the conditioned stimulus (CS) and the unconditioned stimulus (US) converge on the neurons in the lateral amygdala (LA), thereby activating the central amygdala (CeA) and triggering the conditioned response. Interestingly, the amygdala can be associated with various psychiatric disorders, such as anxiety disorders, depression, and even tinnitus. The amygdala is composed of the LA, the basal lateral amygdala (BLA), the basal medial amygdala (BMA), the CeA, the medial amygdala (MeA) and the cortical amygdala (CoA). The lateral amygdala complex (LA, BLA and BMA) is mainly composed of glutamatergic pyramidal neurons (PNs, accounting for 70%-85% of the total neurons), while the CeA mainly contains GABAergic neurons (>90% of the neurons). Glutamate and GABA are the two main neurotransmitters in the amygdala. In addition, the neural activity of the amygdala can also be regulated by various neurotransmitters, neuromodulators and hormones from other areas of the brain, such as acetylcholine (ACh), dopamine (DA), serotonin (5-HT), norepinephrine (NE), and glucocorticoids. The LA receives sensory information from both the thalamus (the fast low road) and the cortex (the slow high road). The PNs in the LA can directly stimulate the projection neurons in the CeA, thereby triggering corresponding behavioral responses, such as urgent response or fear conditioning. The LA PNs can also project to the BLA and BMA for further information processing. The PNs in the BLA/BMA can directly project to the CeA or project to the hippocampus and the prefrontal cortex for processing. The rapid fear conditioning can be achieved through the fast low road. However, the information processing results through the slow high road may modulate or override the initial fear response through the fast low road. More than 90% of the neurons in the CeA are inhibitory neurons, inhibiting neural activity of the brainstem. For example, in the context of freezing behavior, they can inhibit the neural activity of the pre-Bötzinger complex, thereby suppressing breathing. The CeA also contains excitatory neurons (<10%). They can excite neurons in the hypothalamus or in the caudal pontine reticular nucleus, triggering the fight-or-flight response or leading to an enhanced auditory startle response.