d this is associated with pain behaviors. These results suggest that spinal cord VEGFR2 activation by different VEGF isoforms could contribute to nociceptive processing. Despite evidence from clinical studies that demonstrate an involvement of VEGF receptors in pain, and experimental evidence showing that spinal VEGF levels are associated with pain, there are few published findings on the effects of VEGF-A in spinal nociceptive processing. As spinal VEGF-A splicing and isoform expression, and therefore by inference VEGFR2 activation, were altered in PSNI we determined the effect of VEGFR 
antagonism on central nociceptive processing. PTK787 is a tyrosine kinase inhibitor that has non-selective inhibitory actions on VEGFR1 and 2. It is 18-fold more selective for VEGFR1 and 2 over VEGFR3, and has slight selectivity for VEGFR2 over VEGFR1 . In nave rats, systemic VEGFR antagonism with PTK787 increased thermal withdrawal latencies to heat indicating an analgesic effect. To determine the effect of PTK787 on one aspect of central nociceptive processing, we used the formalin test. Injection of formalin into the hind paw allows for the investigation of two distinct phases of acute nociceptive behavior. The initial phase is largely mediated by peripheral nerve activation, whereas the second has both a peripheral and central component. One hour prior to formalin injection, rats were treated with either vehicle or PTK787. The acute phase was unaffected by PTK787 treatment. In contrast the second phase was significantly reduced by systemic PTK787 treatment for both the time of flinching and the number of flinches. These results suggest a central component of VEGFR inhibition. To determine the targets of VEGF-A/VEGFR signaling in nave rats, given the effects of the VEGFR antagonist on the second phase of the formalin test, we recorded electromyographic nociceptive withdrawals to selective nociceptor activation. Fast heating preferentially activates myelinated A-nociceptors and slow heating activates unmyelinated C-nociceptors, both inducing a withdrawal from the stimulus. To determine VEGFR2 specific actions, ZM323881 quinazolin-4-yl]amino]-4-fluoro-2methylphenol) was used locally. ZM323881 which has sub-nanomolar potency and specificity for VEGFR2 , with an IC50 N50 M for VEGFR1 and PDGFR. I.t. ZM323881 186200 193 PSNI Fig. 5. Inhibition of SRPK1 activity in the spinal cord prevents neuropathic pain. Intrathecal SRPIN340 treatment in rats completely prevented mechanical = 3.539), dynamic brush allodynia = 5.526) and cooling allodynia = 7.8) after PSNI in the ipsilateral hind paw. Contralateral hind-paws were not different between groups following mechanical, brush and cooling nociceptive testing. Withdrawal latencies were increased both ipsilaterally = 25.86) and contralaterally = 12.72) following i.t. SRPIN340 treatment.. al., 2002) led to a prolonged increase in the temperature at which the rats withdrew during A-nociceptor stimulation. ZM323881 did not have a significant effect on C-nociceptor withdrawals. These results show that VEGFR2 signaling is mediated, at last in part, by A-nociceptor activation in the spinal cord. Taken together, these results are consistent with the hypothesis that the VEGF-A isoforms may have different functions in the spinal cord, as in the periphery. We tested this by giving VEGF agonists and antagonists intrathecally, and measuring pain R-7128 chemical information behaviors in mice PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19839935 and rats. PTK787 increased both mechanical withdrawal threshold