The effects of intra-VL PAG microinjections of vehicle (0.05% DMSO in ACSF), ONO-DI-004 (0.001, 0.01 and 0.1 pg) alone, or ONO-DI-004 (0.1 pg) in combination with L355677 (0.1 pg) (A and B) or L355677 (0.1, 1 and 10 pg) (C and D), on the spontaneous firing of RVM ON (A and C) or OFF (B and D) cells. Vehicle or drugs were administered at time 0, whereas L 335677 (0.1 pg) was administered 10 min beforehand (A and B). Each point represents the mean ± S.E.M of 6-7 neurons. * indicates a statistically significant difference vs vehicle and° versus ONO-DI-004 (0.1 pg). P values < 0.05 were considered statistically significant.