Disease Progression-dependent Neurobehavioral Phenotypes of Agitation, Anxiety, and Depression in MC903-induced Chronic Itch.

Pruritus is closely associated with anxiety and depression, yet irritability and agitation in chronic itch patients remain poorly characterized in preclinical studies. Using an MC903-induced chronic itch model, we evaluated emotional behaviors across varying durations (7-18 days) and doses (50-100 μM). MC903 induced sequential emotional disturbances: agitation-like behavior emerged early (Day 7), coexisted with anxiety by mid-stage (Day 12), and progressed to depression at late-stage (Day 18). A higher dose (100 μM) accelerated this progression, eliciting agitation and depression with anhedonia within 7 days. We demonstrated that the forced swim test is confounded by cutaneous damage and active pruritus, rendering it unsuitable for affective assessment in skin disease models. Neural mapping identified significant c-Fos activation in the nucleus accumbens (NAc) and central amygdala (CeA) during agitation. Chemogenetic inhibition of GABAergic neurons in both regions reversed agitation-like behaviors, establishing their causal role. Female mice exhibited accelerated and more severe emotional disturbances under conditions producing only mild agitation in males. This study identifies itch-induced agitation, describes a time-, dose-, and sex-dependent emotional progression, and establishes NAc and CeA as causal neural substrates, suggesting specific targets for therapeutic intervention in chronic itch-associated psychiatric comorbidities.