D2.430 - Automated 24-Hour Quantification of Scratching Behavior Reveals Distinct Physiological and Allergic Pruritus Signatures in Mice

Pruritus is a predominant and debilitating symptom in a wide range of diseases, particularly allergic and inflammatory disorders, and markedly impairs quality of life. In experimental animals, pruritus has been evaluated by manual observation of scratching behavior, a method that lacks objectivity and is unsuitable for accurate long-term analysis. 

 To overcome these limitations, we established a deep neural network–based video capture and analysis system named SHIGUSA. This system is capable of continuous long-term video recording and automatic detection of scratching behavior with high sensitivity under both light and dark conditions. Using this system, we performed continuous 24-hour scratching analysis in naïve mice and found that scratching occurred more frequently and for a longer cumulative duration during the light period than during the dark period.

Notably, scratching bouts in the light period were persistent and hard to extinguish compared to those in the dark period, indicating that physiological pruritus changes along the circadian rhythm. Acute administration of four major chemical pruritogens, including histamine, 5-hydroxytryptamine, chloroquine, and lysophosphatidic acid, elicited only transient increases in scratching and did not significantly alter whole-day scratching profiles. In contrast, induction of allergic dermatitis using MC903 or 2,4-dinitrofluorobenzene (DNFB) caused a robust and sustained increase in scratching behavior that persisted for more than 36 hours. Importantly, DNFB treatment significantly shortened the duration of individual scratching bouts, revealing a previously unrecognized qualitative alteration in scratching dynamics under allergic conditions. 

 In summary, we developed a practical and reliable system SHIGUSA for long-term automated scratching analysis and demonstrated distinct temporal and structural features of physiological and pathological pruritus in mice. This approach enables unbiased detection of subtle and chronic scratching phenotypes that have remained inaccessible with conventional observation-based methods and provides a powerful tool for mechanistic and therapeutic studies of pruritus.