Amplification of LPA production by injection of LPA species. (a) Levels of LPA species (18:1, 16:0 and 18:0 LPA) in the spinal dorsal horn were measured by MALDI-TOFMS system at time-course points after i.t. 18:1 LPA injection with 1 nmol. (b) Measurements of LPA species were performed at 3 h after 16:0 or 18:0 LPA injection with 10 nmol. The capital letter “C” represents the control group (naive mice). (c) After i.t. injection of 18:1 LPA (1 nmol), 16:0 LPA (10 nmol) or 18:0 LPA (10 nmol), the pain behavior was evaluated by thermal paw withdrawal test. Results represent the threshold of latency (s) to thermal stimulus. Data represent means ± SEM from experiments using 3-7 mice. *p < 0.05, versus with the control/vehicle group; #p < 0.05, versus with the 0 h-LPA group.