Serum LH levels in WT and GPR54 KO mice in the A.M. and P.M. All mice in the P.M. groups were treated with either vehicle or acyline. Different letters indicate significant difference (p < 0.05; A.M. WT, n = 7; A.M. KO, n = 7; P.M. WT + Veh., n = 9; P.M. KO + Veh., n = 10; P.M. WT + acyline, n = 5; P.M. KO + acyline, n = 8). Error bars indicate SEM. Veh., Vehicle.