Neurons treated with siRNAs targeted to S1PR1 and R3 were not sensitized by S1P but did respond to PGE2. (A) demonstrates representative traces from a sensory neuron treated with combined siRNAs targeted to S1PR1 and R3 (100 nM each); under control conditions, the neuron generated 3 APs. (B) After a 10-min exposure to 1 μM S1P, this neuron fired only 2 APs. (C) A subsequent 10-min exposure to 1 μM PGE2 resulted in the generation of 13 APs. (D) summarizes the effects of S1P and PGE2 exposures after treatment with siRNAs targeted to S1PR1 and R3. S1P failed to augment AP firing, but PGE2 significantly increased the number of APs after 14-, 16-, and 20-min exposures. Results were obtained from eight neurons (control through 12 min), seven neurons at 14 min, and six neurons at 16 and 20 min. Asterisks (*) represent a significant difference between those treatments compared to control (P < 0.05, Kruskal-Wallis ANOVA on ranks with Dunn’s post hoc test). AP - action potential, Cont - control, PGE2 - prostaglandin E2, S1P - sphingosine-1-phosphate.