Amygdalostriatal transition zone neurons encode sustained valence to direct conditioned behaviors

The amygdalostriatal transition zone (ASt) is anatomically poised to provide a shortcut between corticolimbic and basal ganglia circuitry, and mediate behavioral responses to stimuli in parallel with the amygdala. Like the amygdala, the ASt receives converging sensory input from thalamic and cortical pathways. However, the projections of the ASt are distinct from canonical outputs of the amygdala complex, and are integrated with striatal circuits involved in action selection. Despite this intriguing circuit connectivity, the function of the ASt is almost completely unknown. In the present study, we collected cellular resolution recordings of genetically-defined neurons during a valence discrimination task to interrogate the functional role of ASt circuitry, and characterized the transcriptomic profile of the ASt in comparison to neighboring regions. We find that ASt neurons, and specifically, ASt neurons expressing dopamine receptor 2 (D2+), robustly encode sustained conditioned responses to cues of negative valence. Selective inhibition of D2+ ASt neurons was found to cause a striking reduction in conditioned fear responses. We also used single-nucleus RNA sequencing to generate a comprehensive profile of gene expression in ASt neurons, and found that the ASt is genetically distinct from adjacent GABAergic brain regions. RNAscope labelling also confirmed there is a greater proportion of D2+ neurons than D1+ neurons in the ASt, a unique feature compared to other regions of the striatum. Together, our findings provide the first evidence the ASt is a critical structure for encoding learned associations to direct motivated behavior. Comparative single-cell gene expression profiling of pooled amygdalostriatal transition area, central amygdala, dorsal striatum, and tail of striatum samples using snRNA-seq杏仁纹状体过渡区（amygdalostriatal transition zone, ASt）在解剖结构上搭建了皮层边缘系统与基底神经节环路之间的直接通路，可与杏仁核协同介导机体对外部刺激的行为反应。与杏仁核类似，ASt接收来自丘脑与皮层通路的会聚性感觉输入。然而，ASt的神经投射与杏仁核复合体的典型输出存在显著差异，并与参与动作选择的纹状体环路相整合。尽管该环路连接特性颇具研究价值，但目前对ASt的功能几乎一无所知。本研究在效价辨别任务期间，对基因标记神经元开展细胞分辨率记录，以探究ASt环路的功能角色，并对比邻近脑区表征了ASt的转录组谱。研究发现，ASt神经元——尤其是表达多巴胺受体2（D2+）的ASt神经元——能够显著编码针对负性效价线索的持续性条件反应。选择性抑制D2+ ASt神经元可导致条件性恐惧反应大幅减弱。本研究还采用单细胞核RNA测序（single-nucleus RNA sequencing, snRNA-seq）构建了ASt神经元的全面基因表达谱，结果表明ASt在遗传层面与相邻的γ-氨基丁酸能脑区存在显著差异。RNAscope标记技术亦证实，ASt内D2+神经元的比例高于D1+神经元，这与纹状体其他区域的特征截然不同。综上，本研究首次证实ASt是编码习得联结以调控动机性行为的关键结构。本研究通过单细胞核RNA测序，对合并的杏仁纹状体过渡区、中央杏仁核、背侧纹状体及纹状体尾样本开展了比较单细胞基因表达谱分析。