Osteopontin expression and function within the dorsal root ganglion

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Abstract
Osteopontin expression has previously been demonstrated in the adult rat dorsal root ganglion, although its function remains unclear. Here, we demonstrate, using real-time reverse transcription-polymerase (RT-PCR) chain reaction, that osteopontin mRNA expression is increased 1 and 3 weeks following sciatic nerve section (axotomy). Further, immunohistochemical staining suggests that this increase is restricted to neurons already expressing the protein. Osteopontin knock-out animals have significantly increased mechanosensory thresholds in the intact adult compared with the wild-type controls; however no differences in allodynia are noted between genotypes using a model of neuropathic pain. Lastly, exogenous recombinant osteopontin has no effect on neurite outgrowth from adult wild-type sensory neurons, nor were differences in neurite outgrowth observed in osteopontin knock-out animals compared with wild-type controls.