Laboratory of Synaptic Mechanisms, Brain Mind Institute, School of Life Science, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, 1015, Switzerland.
Bernstein Center for Computational Neuroscience, Humboldt University of Berlin, Berlin, 10115, Germany.
J Neurosci. 2020 May 13;40(20):3969-3980. doi: 10.1523/JNEUROSCI.1796-19.2020. Epub 2020 Apr 10.
The amygdala is a brain area critical for the formation of fear memories. However, the nature of the teaching signal(s) that drive plasticity in the amygdala are still under debate. Here, we use optogenetic methods to investigate the contribution of ventral tegmental area (VTA) dopamine neurons to auditory-cued fear learning in male mice. Using anterograde and retrograde labeling, we found that a sparse and relatively evenly distributed population of VTA neurons projects to the basal amygdala (BA). optrode recordings in behaving mice showed that many VTA neurons, among them putative dopamine neurons, are excited by footshocks, and acquire a response to auditory stimuli during fear learning. Combined cfos imaging and retrograde labeling in dopamine transporter (DAT) Cre mice revealed that a large majority of BA projectors (>95%) are dopamine neurons, and that BA projectors become activated by the tone-footshock pairing of fear learning protocols. Finally, silencing VTA dopamine neurons, or their axon terminals in the BA during the footshock, reduced the strength of fear memory as tested 1 d later, whereas silencing the VTA-central amygdala (CeA) projection had no effect. Thus, VTA dopamine neurons projecting to the BA contribute to fear memory formation, by coding for the saliency of the footshock event and by signaling such events to the basal amygdala. Powerful mechanisms of fear learning have evolved in animals and humans to enable survival. During fear conditioning, a sensory cue, such as a tone (the conditioned stimulus), comes to predict an innately aversive stimulus, such as a mild footshock (the unconditioned stimulus). A brain representation of the unconditioned stimulus must act as a teaching signal to instruct plasticity of the conditioned stimulus representation in fear-related brain areas. Here we show that dopamine neurons in the VTA that project to the basal amygdala contribute to such a teaching signal for plasticity, thereby facilitating the formation of fear memories. Knowledge about the role of dopamine in aversively motivated plasticity might allow further insights into maladaptive plasticities that underlie anxiety and post-traumatic stress disorders in humans.
杏仁核是形成恐惧记忆的关键大脑区域。然而,驱动杏仁核可塑性的教学信号的性质仍存在争议。在这里,我们使用光遗传学方法来研究腹侧被盖区(VTA)多巴胺神经元对雄性小鼠听觉线索恐惧学习的贡献。通过顺行和逆行标记,我们发现 VTA 中的一小部分相对均匀分布的神经元投射到基底杏仁核(BA)。在行为小鼠中的 optrode 记录显示,许多 VTA 神经元,其中包括推定的多巴胺神经元,被足部电击激发,并在恐惧学习期间对听觉刺激产生反应。在多巴胺转运蛋白(DAT)Cre 小鼠中的 cfos 成像和逆行标记的结合表明,BA 投射神经元的绝大多数(> 95%)是多巴胺神经元,并且 BA 投射神经元在恐惧学习协议的音-足电击配对过程中被激活。最后,在足部电击期间沉默 VTA 多巴胺神经元或其轴突末端,会降低 1 天后恐惧记忆的强度,而沉默 VTA-中杏仁核(CeA)投射则没有影响。因此,投射到 BA 的 VTA 多巴胺神经元通过对足部电击事件的显着性进行编码,并将此类事件信号传递到基底杏仁核,从而有助于恐惧记忆的形成。动物和人类已经进化出强大的恐惧学习机制,以实现生存。在恐惧条件反射中,一种感觉线索,例如音调(条件刺激),开始预测一种本能的厌恶刺激,例如轻度足部电击(非条件刺激)。非条件刺激的大脑代表必须充当教学信号,以指导恐惧相关大脑区域中条件刺激代表的可塑性。在这里,我们表明投射到基底杏仁核的 VTA 中的多巴胺神经元有助于这种可塑性的教学信号,从而促进恐惧记忆的形成。关于多巴胺在厌恶动机可塑性中的作用的知识可能会进一步深入了解人类焦虑和创伤后应激障碍的适应不良可塑性。