# GPR55 and GPR119 Receptors Contribute to the Processing of Neuropathic Pain in Rats
## 2 Results  
### Controls  
L5-L6 spinal nerve ligation produced tactile allodynia in the ipsilateral left hind paw; a significant reduction in the basal 50% paw withdrawal threshold was observed in L5-L6 spinal nerve-ligated rats (3.3 \(\pm\) 0.7 g) after 14 days of surgical procedure with respect to naive rats (14.8 \(\pm\) 0.5 g) or sham rats (13.8 \(\pm\) 1.6 g). Moreover, the intrathecal injection of the vehicle (20 uL/rat) did not statistically modify the 50% paw withdrawal threshold of L5-L6 spinal nerve-ligated rats (2.6 \(\pm\) 0.9 g), indicating that any change in the 50% paw withdrawal can be attributed to the pharmacological treatment (Figure 1).  
Figure 1: Mechanical allodynia induced by spinal nerve L5-L6 ligation. (**A**) Time courses of 50% hind paw withdrawal threshold in naïve (white circles), sham (black circles) or L5-L6 spinal nerve-ligation-induced neuropathic (grey circles) rats. (**B**) Percentage of maximum effect possible (%MPE) calculated from the time courses with the different groups. Data represent the mean \(\pm\) SEM of six animals per group.  
Antiallodynic Effect of Selective Antagonist GPR55 (CID16020046) and Selective Agonist GPR119 (AS1269574) in L5-L6 Spinal Nerve-Ligated Rats  
The role of spinal GPR55 and GPR119 receptors in the processing of L5-L6 spinal nerve ligation-induced neuropathic pain was tested by the intrathecal injection of selective antagonist GPR55 (CID16020046) and selective agonist GPR119 (AS1269574). Intrathecal administration of CID16020046 (1-300 \(\mathrm{\SIUnitSymbolMicro  
GPR55 antagonist CID16020046 and the GPR119 agonist AS1269574, respectively. The antiallodynic effect induced by the selective GPR55 antagonist CID16020046 (300 \(\upmu\)g/rat, i.t.) was significantly prevented by increasing doses of the agonist O1602 (30-300 \(\upmu\)g/rat, i.t.), as shown in Figure 3A,C. In addition, O1602 did not modify the 50% paw withdrawal threshold in L5-L6 spinal nerve-ligated rats when the drug was administered individually at the highest tested dose (300 \(\upmu\)g/rat, i.t.). On the other hand, the reduction in the allo-dynia produced by intrathecal administration of the selective GPR119 agonist AS1269574 (300 \(\upmu\)g/rat, i.t.) was reversed, in a dose-dependent manner, with increasing doses of G-protein antagonist peptide (0.001-1 ng/rat, i.t.), as shown in Figure 3B,D. Interestingly, G-protein antagonist peptide (1 ng/rat, i.t.) was not able to decrease the 50% paw withdrawal threshold when injected separately, which suggests a selective effect against the activation of spinal GPR119 receptors when co-administered with AS1269574.  
To discount the participation of systemic effects that could affect the nociceptive evaluation, plasmonic glucose levels were measured after spinal administration of CID-16020046 (300 \(\upmu\)g), O-1602 (300 \(\upmu\)g), AS-1269574 (300 \(\upmu\)g) or G-PP (1 ng) at the same times that allodynia was evaluated in the rats. Moreover, these doses were also evaluated in the rotarod-test to rule out a possible motor impairment induced by the drugs. In this regard, none of the drugs affected plasmonic glucose levels or motor coordination at the highest doses tested.  
Figure 3: Effect of increasing doses of O-1602 (selective GPR55 agonist; (**A**,**C**)) and G-protein antagonist peptide (**B**,**D**) on antiallodynic effect induced by CID-16020046 (selective GPR55 antagonist; (**A**,**C**)) and AS-1269574 (selective GPR119 agonist; (**B**,**D**)), respectively, in L5-L6 spinal nerve ligation-induced neuropathic rats. Data represent the mean \(\pm\) SEM of six animals per group. * Significantly different from the vehicle group and # significantly different from CID-16020046 or AS-1269574 group by one-way analysis of variance, followed by post hoc Dunnett’s test with \(p<0.05\). Abbreviations: %MPE = percentage of maximum effect possible.