A method to enhance the magnitude of tactile hypersensitivity following spinal nerve ligation in rats

Rosa Maria A Simmons, Beth Forster, Wenhong Guo, Kelly L Knopp
Journal of Neuroscience Methods 2014 August 15, 233: 50-3

BACKGROUND: The rat L5/L6 spinal nerve ligation model (SNL) has been widely used to investigate putative analgesics. Pursuit of novel therapies in preclinical settings requires models with consistent and reproducible phenotypes.

NEW METHOD: We assessed the effects of repetitive stimulation of the hindpaws of SNL and Sham surgery rats during the 2 weeks immediately after surgery on the overall rate of achieving tactile hypersensitivity, as well as the magnitude of the hypersensitivity compared to unprimed rats. Beginning on day 2 post-surgery, and continuing on alternate days for a total of seven sessions, animals underwent light brushing/tapping (termed priming) of the hindpaws ipsilateral and contralateral to surgery.

RESULTS: Priming the ipsilateral hindpaw enhanced the magnitude of tactile hypersensitivity such that the baseline withdrawal threshold (BWT) for primed SNL animals was significantly lower than unprimed SNL animals over post-surgical days 15-29. BWT was not different between primed and unprimed Sham rats. The percentage of SNL primed animals meeting the a priori criterion for tactile hypersensitivity of paw withdrawal threshold less than 2.0 grams was 98.9%±1.1%.

COMPARISON WITH EXISTING METHOD: SNL rats that did not receive stimulation (unprimed) showed significantly higher baseline hypersensitivity when evaluated on days 15-29, exemplified by only 34.5%±7.2% meeting the established <2.0g criterion.

CONCLUSION: Our data indicate that tactile priming during the 2 weeks immediately after SNL surgery enhances the magnitude of tactile hypersensitivity in the SNL model, and provide an optimized assay for evaluating putative analgesics.

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