LOSS OF RXFP3 RECEPTORS IN SOMATOSTATIN-EXPRESSING NEURONS ATTENUATES ANXIETY, DEPRESSION, FEAR-LIKE BEHAVIORS, AND PAIN SENSITIVITY

The neuropeptide relaxin-3 and its primary receptor, RXFP3, constitute a highly conserved signaling system predominantly expressed in brain regions involved in stress and emotional processing. While RXFP3 is widely distributed, its specific expression on somatostatin-expressing neurons suggests a localized mechanism for modulating inhibitory circuits that regulate behavioral outputs. To investigate this, we generated and performed comprehensive behavioral phenotyping and whole-brain activity mapping of conditional knockout (cKO) mouse strain, which lacks RXFP3 receptors exclusively on somatostatin neurons. Using a battery of paradigms including open field (OF), T-maze, three chambers, elevated-plus maze (EPM), light-dark box (LDB), splash test (ST), forced swimming test (FST), context fear conditioning, and nociceptive assays, we evaluated motor function, cognition, and emotional states. Additionally, brains underwent AdipoClear+ tissue clearing and c-Fos staining, followed by light-sheet microscopy and brain atlas registration to quantify regional neuronal activity. While cKO mice exhibited unimpaired basal locomotion, sociability, and spatial working memory, they displayed a robust anxiolytic phenotype, characterized by significantly increased time in the center of the OF, open arms of the EPM, and the light compartment of the LDB. cKO mice also showed reduced depressive-like behavior through increased grooming in the ST and decreased immobility in the FST. Additionally, cKO mice showed impaired fear memory consolidation and significant thermal and mechanical hypoalgesia. These changes correlated with a general downregulation of c-Fos in brain areas related to negative emotions and pain. Collectively, our findings suggest that RXFP3 signalling within somatostatin neurons is a critical modulator of anxiety, stress-coping, and pain processing.