Effects of Psychological Stress on Spontaneous Itch and Mechanical Alloknesis of Atopic Dermatitis.

Atopic dermatitis (AD), a chronic inflammatory skin disease, manifests as an intractable itch. Psychological stress has been suggested to play a role in the onset and worsening of AD symptoms. However, the pathophysiological relationships between psychological stressors and cutaneous manifestations remain unclear. To elucidate the mechanisms underlying the stress-related exacerbation of itch, we investigated the effects of water stress, restraint stress and repeated social defeat stress on itch-related scratching behaviour, mechanical alloknesis and dermatitis in male NC/Nga mice with AD-like symptoms induced by the repeated application of ointment containing Dermatophagoides farina body. NC/Nga mice with AD-like symptoms were subjected to water stress, restraint stress and repeated social defeat stress, and their scratching behaviour, sensitivity to mechanical stimuli (mechanical alloknesis) and severity of  dermatitis were evaluated. Social defeat stress+ Dermatophagoides farina body-treated mice exposed to stress showed slower improvements in or the exacerbation of AD-like symptoms, including dermatitis and itch. In the mechanical alloknesis assay, the mechanical alloknesis scores of social defeat stress+ Dermatophagoides farina body-treated mice exposed to stress were significantly higher than those of non-exposed social defeat stress+ Dermatophagoides farina body- and social defeat stress-treated mice. These results suggest that psychological stress delays improvements in dermatitis by exacerbating itch hypersensitivity in AD.