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.