1. Targeted delivery of NPY into dorsal root ganglion reduces pain- related behavior following intraplantar carrageenan injection Sandra Kostic, Livia Puljak, Damir Sapunar Laboratory for Pain Research, Department of Anatomy, Histology and Embryology, University of Split School of Medicine Neuropeptide Y (NPY) plays an important role in pain modulation at different levels of the central nervous system. The aim of this study was to investigate if targeted delivery of NPY and its antagonists to DRG can modulate pain related behavior in rats with carrageenan-induced inflammation. In addition we analyzed their effects on GFAP expression in DRG and dorsal horn (DH). INTRODUCTION MATERIALS AND METHODS Experimental animals and surgical procedure: Simultaneously with carrageenan induced inflammation, male Sprague-Dawley rats were given injections of NPY, NPY1 (BIBO3304) and NPY2 (BIIE0246) antagonists directly to L5 DRG. Rats were assigned to one of the following groups: control group, carrageenan group with saline delivered directly to DRG, three carrageenan injected groups with DRG injection of NPY, BIBO3304 or BIIE0246. Behavioral testing was performed on the day preceding the carrageenan injection, 5 hours after, on the 1st, 5th and 8th day following the injection. We measured changes in sensory test responses between ipsi- and contralateral paws over time using heat and cold stimulus, pin prick test and von Frey fibers. Immunohistochemistry: Eight days following the injections, the L5 ganglion and corresponding spinal cord segment were removed, sectioned and treated with rabbit anti-GFAP polyclonal antibody. RESULTS Carrageenan significantly increased left hindpaw size compared to hindpaw injected with saline (control). Injection of carrageenan did not induce significant change in heat or cold withdrawal latency (A and C). DRG targeted delivery of NPY exacerbated cold hypersensitivity (B) but did not change withdrawal latency to heat stimulus (D). Cold and heat withdrawal threshold were not influenced by Y1 or Y2 blockade (B and D). Each value represents the mean difference between left and right paws. Data are presented as mean ± SEM. Asterisk denotes significant difference from baseline. Legend: Carr–carrageenan; ipl–intraplantar; igl–intraganglionic. Intraplantar carrageenan injection increased astrocyte activation in dorsal horn compared to control (saline injection). NPY injection produced similar activation as did carrageenan, while BIIE decreased number of GFAP-positive astrocites compared to control and carrageenan-injected animals. Legend: DREZ – dorsal root entry zone NPY increased GFAP expression in DRG satellite cells but statistical analysis of did not provide conclusive evidence of this effect (scale bar: 50 μm). Carrageenan produced significant changes in withdrawal and hyperalgesic responses (A and C). Mechanical allodynia was observed only 5h after carrageenan injection (E). DRG targeted delivery of NPY performed simultaneously with carrageenan injection exacerbated withdrawal response (B). Mechanical allodynia in NPY injected rats was enhanced but in the same manner as in carrageenan/saline group (F). Application of BIBO3304 into DRG produced change in withdrawal response, 5 hours and 5 days after the injection; as did the application of BIIE0246, 5 hours, on the 1st and 5th day (B). Each value represents the mean difference between left and right paws. Data are presented as mean ± SEM. Legend: * - significant difference from control values in carageenan and NPY injected rats; # - significant difference form control values in BIBO injected rats; + - significant difference form control values in BIIE injected rats. CONCLUSION Our results demonstrate that NPY reduces withdrawal threshold when injected in DRG of rats with carrageenan-induced inflammation. However, targeted delivery of NPY to DRG additional exacerbated cold latency induced with intraplantar carrageenan injection. NPY antagonists reduced the effect of carrageenan and NPY in the modality specific manner. Poster session date 9/1/2010 Supported by MZOS grant no. 216-2160528-0522 PW 255