Characterisation of the pruritus responses and pruritic behaviours in an interleukin 31‐induced canine model of pruritus

Abstract Background Intravenous administration of interleukin (IL)‐31 in healthy dogs has been used as a model to assess antipruritic drugs. However, there is no known in‐depth characterisation of pruritic behaviours, and the repeatability of the IL‐31‐induced pruritus in the individual dogs is currently unknown. Objectives To evaluate the immediate/delayed pruritus responses and the pruritic behaviours observed in the IL‐31‐induced pruritic model in healthy dogs after repeated IL‐31 injections. Animals Fifteen healthy laboratory beagles. Methods All dogs were video‐recorded for 270 min after two intravenous recombinant IL‐31 injections (1.75 μg/kg) and vehicle (phosphate‐buffered saline, control) injections, respectively; interventions were randomised and performed with a 2 week wash‐out period. Two blinded investigators reviewed the pruritic behaviours of all video recordings. Results Both canine IL‐31 (IL‐31_01, IL‐31_02) injections significantly increased pruritic seconds and categorical minutes (‘YES’/‘NO’ behaviour per discrete 1 min interval) in healthy dogs compared with both vehicle groups (Vehicle_01, Vehicle_02). The second intravenous canine IL‐31 (IL‐31_02) administered 14 days after the first IL‐31 injection induced a significant increase in pruritic seconds ( p = 0.021) and not pruritic categorical minutes ( p = 0.231). An increase in pruritic seconds was observed in both IL‐31 groups in the first 30 min post‐administration, while there was no significant difference between IL‐31 and vehicle groups. Conclusions and Clinical Relevance In conclusion, intravenous IL‐31 reproducibly induces itch responses in dogs. Future evaluations of the canine IL‐31 pruritic model should assess total pruritic behaviours in seconds rather than using a biased ‘YES/NO’ behaviour per 1 min scoring system.