F2RL1 and major depressive disorder: Increased brain cytokine levels are regularly reported in rodent models of sickness and depression-like behaviour (Dantzer 2017; Takahashi et al. 2018); therefore, the observed increases in IL-1β mRNA following AC injection are consistent with it playing a role in the PAR2-induced behavioural changes and with elevated cytokine levels reported for other PAR2-related inflammatory disorders (McCulloch et al. 2018; Chandrabalan and Ramachandran 2021).