F2RL1 and major depressive disorder: We have previously shown that protease-activated receptor 2 (PAR2) deletion results in impaired LPS-induced sickness behaviour (Abulkassim et al. 2016) and that PAR2 activation impairs synaptic transmission in the hippocampus (Gan et al. 2011), a brain region proposed to play a key role in depression (Malykhin and Coupland 2015; Boku et al. 2018).