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doi: 10.1097/ALN.0b013e3182a95164
Pain Medicine

Intrathecal Substance P-Saporin in the Dog: Distribution, Safety, and Spinal Neurokinin-1 Receptor Ablation

Wiese, Ashley J. D.V.M.*; Rathbun, Michael; Butt, Mark T. D.V.M.; Malkmus, Shelle A. B.S., R.V.T.; Richter, Philip J. D.V.M.§; Osborn, Kent G. D.V.M.; Xu, Qinghao Ph.D.#; Veesart, Samantha L. A.H.T.; Steinauer, Joanne J. B.S.; Higgins, Denise**; Lappi, Douglas A. Ph.D.††; Russell, Brian B.S.‡‡; Yaksh, Tony L. Ph.D.§§

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Background: Neurokinin-1 receptors (NK1-rs) located on superficial dorsal horn neurons are essential for integration of nociceptive input. Intrathecal injection of substance P-saporin (SP-SAP) leads to local loss of spinal NK1-r (+) neurons suggesting its potential as a therapeutic agent for chronic pain. The authors determined, in a canine model, effects of lumbar intrathecal SP-SAP.
Methods: Distribution of SP-SAP and Saporin was determined in plasma, lumbar cerebrospinal fluid, and tissue. Safety of intrathecal SP-SAP was determined in four groups (six dogs each) administered 0 (0.9% saline), 1.5, 15, or 150 µg SP-SAP through lumbar intrathecal catheters. Behavioral, physiologic, and biochemical variables were assessed. Spinal tissues were collected at 7 and approximately 90 days, or earlier if significant morbidity developed, and analyzed for NK1-r (+) neuron loss and histopathology.
Results: SP-SAP and Saporin were detectable in lumbar cerebrospinal fluid for up to 4 and 24 h, respectively. Animals receiving intrathecal saline, 1.5, or 15 µg of SP-SAP showed no persistent neurologic deficits. Three animals receiving 150 µg of SP-SAP developed pelvic limb paraparesis and were euthanized prematurely. Immunohistochemistry and in situ hybridization cell counts confirmed a significant reduction in NK1-r (+) in superficial dorsal horn neurons from lumbar spinal cord after intrathecal administration of 15 and 150 µg of SP-SAP. A significant loss of NK1-r neurons in the lumbar ventral horn occurred only with 150-µg SP-SAP.
Conclusion: Intrathecal 15-µg SP-SAP reduced dorsal, but not ventral, NK1-r (+) neurons at the spinal level of delivery with minimal side effects, whereas 150-µg SP-SAP resulted in motor neuron toxicity.

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