Intrathecal Noggin administration in rats temporally ameliorates mechanical allodynia induced by a chronic constriction injury

Chronic intractable neuropathic pain after central or peripheral nervous system injury remains refractory to therapeutic intervention. Using microarray and RT-qPCR methods, we found that Noggin mRNA is downregulated in the lumbar enlargement 2 weeks after chronic constriction injury (CCI) in rats. Eight-week-old female Sprague Dawley rats were used for the CCI model. Two weeks after CCI, rats underwent a laminectomy at L5 under halothane anesthesia, and a silicone tube connected to an osmotic minipump was inserted intrathecally for 14 days. Rats were administered Noggin ranging from 10 ng/ml to 10 μg/ml. Phosphate buffered saline (PBS) was used as a control. The time course of mechanical allodynia was assessed for 5 weeks using von Frey filaments. An ANOVA showed that rats administered Noggin at 2 μg/ml had significantly less mechanical allodynia compared with controls. We next compared the effect of intrathecal administration (14 days) of Noggin (2 μg/ml), bone morphogenetic protein 4 (BMP4; 2 μg/ml), or BMP4 (μg/ml) + Noggin (μg/ml) with controls. Only Noggin administration significantly reduced mechanical allodynia in the CCI model. Fluorescence immunohistochemistry indicated that Noggin administration decreased astrocyte accumulation in the dorsal horn compared with PBS after administration for one week. BMP4-driven conversion of oligodendrocyte progenitor cells (OPCs) to type 2 astrocytes is inhibited by Noggin Hampton et al. (2007) . We speculated that Noggin administration inhibits the conversion of OPCs to astrocytes, and decreases glial fibrillar acidic protein expression. This histological condition could decrease neuropathic pain.