D1 RECEPTOR–MEDIATED DOPAMINERGIC CONTROL OF VIP INTERNEURONS FOR PAIN MODULATION IN THE ANTERIOR INSULAR CORTEX

Pain is a subjective and emotional experience that emerges from distributed brain activity integrating sensory and affective components. The anterior insular cortex (AIC) plays a central role in this process, and dopaminergic signaling through D1 receptors (D1R) in the AIC has been associated with pain modulation. Nevertheless, the cellular identity and functional properties of D1R-expressing neurons within AIC microcircuits remain insufficiently characterized.
Here, we combined anatomical, electrophysiological and behavioral approaches to characterize D1R-expressing neurons in the mouse AIC. Using D1R-Tomato transgenic mice, we observed that D1R-positive neurons are differentially distributed across cortical layers, with superficial layers enriched in inhibitory interneurons and deeper layers containing both pyramidal neurons and interneurons. Moreover, immunohistochemical analyses revealed that the majority of superficial D1R-expressing interneurons co-express vasoactive intestinal peptide (VIP), while lacking markers of parvalbumin or somatostatin interneuron populations. Consistent with this molecular profile, morphological reconstructions showed bipolar and multipolar architectures typical of VIP interneurons. In parallel, ex vivo whole-cell recordings demonstrated that activation of D1 receptors increases the excitability of D1R-positive neurons, supporting a direct dopaminergic influence on this cell population.
Finally, using c-fos as a marker, we observed a robust activation of AIC D1R-expressing neurons during acute visceral pain.
Together, these findings provide a comprehensive anatomical and functional characterization of D1R-expressing neurons in the AIC and link their engagement to cortical processing during acute pain.