Up–Down thresholds are calculated in two ways-using mathematical formulas established by Dixon ( Chaplan et al., 1994 Dixon, 1965, 1980) or the 50% response threshold ( Lindsey et al., 2000). The Up–Down method determines the threshold by alternating VFHs according to the presence or absence (pattern) of paw withdrawal. The ascending method applies VFHs in consecutive, ascending order until paw withdrawal occurs at least 50% of VFH applications ( Chaplan et al., 1994). The two remaining paradigms define allodynia as a marked reduction in tactile thresholds. To be considered allodynia, more responses to sub-threshold stimulation must occur relative to normal. The most common method relies on frequency of responses to sub- or supra-threshold stimulus. Ohio State University electromagnetic device (0.3, 0.5, 0.7, 0.9, 1.1, 1.25, 1.3 mm cord displacement)Ĭurrently, three methods detect below-level allodynia after experimental SCI by manipulating the frequency, quality or intensity of von Frey hair monofilaments (VFH) applied to the hindpaw ( Table 1). New York University/MASCIS Device 6.25, 12.5, 25, 50 mm wt. Whether acute assessments can be developed remains unclear but represents an important, uncharacterized time point in below-level neuropathic pain development. By necessity then, the earliest readout of sensation occurs weeks after SCI. To date only one procedure appears to be standardized-all testing paradigms require hind limb motor control before testing begins. However, many sensory testing approaches exist for SCI often with little description of key parameters like acclimation methods, testing environment, initial VFH force and number of VFH applications ( Table 1). Thus, standardized procedures which control seemingly unrelated factors are especially important in SCI testing. naturally-occurring diurnal fluctuations in activity ( Gobel and Cordes, 1990 Lemmer, 1991) and experimentally-induced paralysis or paresis). Aversive paw withdrawal to tactile stimulation serves as a proxy for pain but factors which influence movement will confound the measurement of sensation (i.e. While several models of SCI exist, the requisite cognitive and attentive aspects of pain in each model remain unclear. Allodynia, a common form of SCI-induced pain, occurs when normally innocuous stimuli produce painful responses. Over two-thirds of individuals with spinal cord injury (SCI) experience devastating effects of neuropathic pain on their daily lives ( Crozier et al., 1991 Finnerup et al., 2001 Siddall et al., 2003, 1999a Widerstrom-Noga et al., 2001). Early detection of allodynia in experimental SCI will allow identification of mechanisms responsible for pain development and determine targets for therapeutic interventions. Thus, standardized testing early after SCI using the dorsal VFH test or later using 10 stimuli in the Up–Down test produces valid measures of tactile sensation across many SCI severities. Acute dorsal VFH thresholds collected before recovery of hindlimb weight support accurately predicted plantar VFH thresholds measured at late timepoints ( χ 2=8.479 p<0.05). The new test uses dorsal VFH stimulation and is independent of trunk or hindlimb control. Importantly, distraction of SCI-rats with food revealed differential decay of thresholds than when distraction is not provided. Ten Up–Down VFH applications yielded stable thresholds reducing the risk of threshold decay and unnecessary exposure to painful stimuli. The most efficient and valid procedures that maintain high sensitivity and specificity were identified. To determine tactile thresholds, von Frey hairs (VFH) were applied in Up–Down or ascending order to the dorsal or plantar hindpaw. One hundred fifty-six Sprague–Dawley rats received T8 laminectomy or mild to moderate SCI using the OSU SCI device (0.3 mm to 1.3mm cord displacement). Therefore, we validated sensory threshold assessment after SCI and developed a novel assessment of allodynia prior to motor recovery in a rat SCI model. Assessment of SCI-induced allodynia is not standardized across labs, making interpretation of results difficult. Measuring the development of allodynia in rodent models of SCI is challenging due to spinal shock and marked motor impairments. Spinal cord injury (SCI) impairs sensory systems causing allodynia.
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