An analysis of changes in sensory thresholds to mild tactile and cold stimuli after experimental spinal cord injury

Changes in sensory function including chronic pain and allodynia are common sequelae of spinal cord injury (SCI) in humans. The present study documents the ex-tent and time course of mechanical allodynia and cold hyperalgesia after contusion SCI in the rat using stimulation with graded von Frey filaments (4.97-50.45 g force) and ice probes. Fore- and hind-paw withdrawal thresholds to plantar skin stimulation were determined in rats with a range of SCI severities (lO-g weight dropped from 6.25, 12.5, or 25 mm using the MASCIS injury device); animals with 25-mm injuries most consistently showed decreased hind-paw withdrawal thresholds to touch and cold, which developed over several weeksafter surgery. Stimulation of the torso with graded von Frey hairs was performed at specified locations on the back and sides from the neck to the haunch. Suprasegmental responses (orientation, vocalization, or escape) to mechanical stimulation of these sites were elicited infrequently in the laminec-tomy control rats and only during the first 3 weeks after surgery, whereas in 25-mm SCI rats, such responses were obtained for the entire 10 weeks of the study. These data suggest that rats with contusion SCI may exhibit sensory alterations relevant to human spinal cord injuries. Key Words: Spinal cord injury-Chronic pam-e-Allody-nia-Hyperalgesia.. Chronic pain after traumatic spinal cord injury (SCI) IS a major clinical problem that affects most SCI patients (I,2). The onset of chronic pain is typically within-6 mOnths of injury and may persist throughout the patient'