PAFR and Neuropathic Pain Figure 2. LOX inhibitors do not prevent the development of tactile allodynia after nerve injury. A, B. The 5-LOX inhibitor AA-861 (20 nmol/10 ml) (A) and the 12- and 15-LOX inhibitor baicalein (20 nmol/10 ml) (B) administered through a catheter whose tip was positioned near the L5 DRG once daily for 14 days did not suppressed the development of nerve injury-induced tactile allodynia. **p,0.01, ***p,0.001 compared with the threshold of the vehicle-treated group on day 0. {{p,0.01, {{{p,0.001 compared with the threshold of the inhibitor-treated group on day 0. All data are presented as mean 6 SEM of the paw withdrawal threshold of five animals. doi:10.1371/journal.pone.0010467.g002 antagonists to nerve-injured rats because inhibitors of PAF and LPA biosynthetic enzymes are not available. We injected the PAFR antagonist CV-3988 [29] and the LPA1R and LPA3R antagonist Ki16425 [30] near the L5 DRG and found that CV- 3988 and Ki16425 significantly reduced the development of tactile allodynia (CV-3988, p,0.001; Ki16425, day 3: p,0.01, day 7: p,0.001, day 14: p,0.05) (Fig. 3A, B). By contrast, such suppressing effect of CV-3988 on allodynia development was not observed when CV-3988 was administered to the lumbar enlargement of the spinal cord (where injured DRG neurons project) (Fig. S1), suggesting that the anti-allodynic effect of the PAFR antagonist may predominantly involve PAFRs expressed in the DRG rather than in the spinal cord. In addition, CV-3988 treatment did not suppress thermal hyperalgesia (Fig. S2). Since our previous study showed that acute inhibition of cPLA2 produces an alleviation of existing tactile allodynia [5], we then examined whether pharmacological blockade of PAFRs and LPARs could also be effective in treating existing allodynia. A single administration of CV-3988 near the DRG 7 days after nerve injury also partially reduced the expression of tactile allodynia within 60 min (p,0.001) (Fig. 4A), whereas the decreased paw withdrawal threshold at day 7 after nerve injury was not reversed Figure 3. PAFR and LPAR antagonists suppress the development of tactile allodynia by injury to the L5 spinal nerve. A, B. Administration of PAFR antagonist CV-3988 (10 nmol/10 ml) (A) and the LPAR antagonist Ki16425 (10 nmol/10 ml) (B) through a catheter whose tip was positioned near the L5 DRG once daily for 14 days after nerve injury suppressed the development of tactile allodynia. **p,0.01, ***p,0.001 compared with the threshold of the vehicle-treated group on day 0. {{p,0.01, {{{p,0.001 compared with the threshold of the antagonist-treated group on day 0. #p,0.05, ##p,0.01, ###p,0.001 compared with the threshold of the vehicle-treated group at each time point. All data are presented as mean 6 SEM of the paw withdrawal threshold of five to eight animals. doi:10.1371/journal.pone.0010467.g003 PLoS ONE | www.plosone.org 3 May 2010 | Volume 5 | Issue 5 | e10467