Intracerebroventricular injection of phospholipases A2 inhibitors modulates allodynia after facial carrageenan injection in mice

The present study was carried out, using inhibitors to secretory phospholipase A2 (sPLA2, 12-epi-scalaradial), cytosolic phospholipase A2 (cPLA2, AACOCF3), or calcium-independent phospholipase A2 (iPLA2, bromoenol lactone), to compare possible contributions of central nervous PLA2 isoforms to the development of allodynia after facial carrageenan injection in mice. C57BL/6J (B6) mice showed increased responses to facial stimulation using a von Frey hair (1 g force), at 8 h, 1 day, and 3 days after facial carrageenan injection. On the other hand, BALB/c mice did not show increased responses at any of the time points. In both B6 and BALB/c mice, intracerebroventricular injection of inhibitors to each of the three PLA2 isoforms significantly reduced responses to von Frey hair stimulation at 8 h and 1 day after facial carrageenan injection, but at 3 days after injection, only the sPLA2 inhibitor had an effect. Since BALB/c mice did not show increased responses after facial carrageenan injection, the reduction in responses actually indicates that there is loss of normal sensitivity to von Frey hair stimulation after intracerebroventricular injection of each of these inhibitors, in this strain of mice. The effects of PLA2 inhibitors are unlikely to be due simply to inhibition of arachidonic acid generation, since intracerebroventricular injection of arachidonic acid also had an anti-nociceptive effect. The above results support an important role of central nervous PLA2s in neurotransmission and pain transmission.