β-Arrestin–dependent ERK signaling reduces anxiety-like and conditioned fear–related behaviors in mice

Abstract

β-Arrestin signaling may mediate the fear- and anxiety-relieving effects as well as adverse events of opioids. Arresting fear and anxiety Opioid receptors activate either G proteins or β-arrestins. Many adverse side effects associated with opioid use are mediated by β-arrestins. Therefore, drugs that bias opioid receptor signaling toward G protein–mediated pathways are preferred for treating pain. However, Ko et al. found that β-arrestin–biased drugs may have potential for treating fear and anxiety. Natural and synthetic opioids differentially altered such behaviors in mice through G protein– and β-arrestin–specific signaling in various brain regions that indicated distinct and compensatory functions of the β-arrestin isoforms. The findings begin to reveal a context-specific aspect of opioid receptor signaling in neurological function and animal behavior. G protein–coupled receptors (GPCRs) are implicated in the regulation of fear and anxiety. GPCR signaling involves canonical G protein pathways but can also engage downstream kinases and effectors through scaffolding interactions mediated by β-arrestin. Here, we investigated whether β-arrestin signaling regulates anxiety-like and fear-related behavior in mice in response to activation of the GPCR δ-opioid receptor (δOR or DOR). Administration of β-arrestin–biased δOR agonists to male C57BL/6 mice revealed β-arrestin 2–dependent activation of extracellular signal–regulated kinases 1 and 2 (ERK1/2) in the dorsal hippocampus and amygdala and β-arrestin 1–dependent activation of ERK1/2 in the nucleus accumbens. In mice, β-arrestin–biased agonist treatment was associated with reduced anxiety-like and fear-related behaviors, with some overlapping and isoform-specific input. In contrast, applying a G protein–biased δOR agonist decreased ERK1/2 activity in all three regions as well as the dorsal striatum and was associated with increased fear-related behavior without effects on baseline anxiety. Our results indicate a complex picture of δOR neuromodulation in which β-arrestin 1– and 2–dependent ERK signaling in specific brain subregions suppresses behaviors associated with anxiety and fear and opposes the effects of G protein–biased signaling. Overall, our findings highlight the importance of noncanonical β-arrestin–dependent GPCR signaling in the regulation of these interrelated emotions.