Characterization and Optogenetic Manipulation of the Affective Itch Circuit in Mouse Models of Itch

Itch consists of both sensory and affective components. For chronic itch patients, the affective component of itch affects both quality of life (leading to psychological comorbidities) and disease prognosis (by promoting scratching of itchy skin). We found that acute and chronic itch stimuli induced anxiety-like behavior and increased activity (c-Fos expression) in the amygdala in adult male C57BL/6 mice. Itch stimuli also increased activity in projection areas to the amygdala, suggesting that these regions form a circuit for affective itch processing. Selective optogenetic activation of histamine-responsive amygdala neurons in adult male and female Fos:CreER^T2;R26^Ai14 mice using the Targeted Recombination in Active Populations system enhanced both scratching and anxiety-like behavior. These results highlight the importance of itch-responsive amygdala neurons in modulating itch-related affect and behavior.