Changes in neuronal receptive field characteristics in caudal brain stem following chronic spinal cord injury

Chronic spinal cord injury pain is poorly understood and, thus, not effecti vely relieved by traditional treatments. In the present study, a variety of partial, severe and sham chronic spinal lesions were made in 31 male rats at spinal level TS, During routine care/handling and brief behavioral testi ng of the animals throughout the 30-day recovery period, the majority of th ose with severe contusion injuries (verified histologically) showed signs o f mechanical hypersensitivity on the dorsolateral trunk just rostral to the level of injury (i.e., upper thoracic territory). Terminal electrophysiolo gical experiments were performed on ail rats (urethane anesthesia). Single unit recordings were made at two supraspinal locations within the caudal br ainstem, the nucleus reticularis gigantocellularis and nucleus reticularis gigantocellularis pars alpha, Neurons in these areas normally receive bilat eral nociceptive somatovisceral inputs from many parts of the body. Seventy three percent of the animals with severe contusion injuries developed nove l low-threshold neuronal responses to stimulation of the dorsolateral trunk (upper thoracic territory). This amount was significantly greater than for animals with more moderate spinal lesions (dorsal or lateral hemisection; 29% and 25%, respectively) or sham controls (0%), These data suggest (1) th at the spinal contusion is a reliable model for studies of the neural mecha nisms that underly central spinal cord injury-related pain and (2) that the caudal brainstem is one supraspinal location where neurons undergo signifi cant changes in responsiveness following severe chronic spinal cord injury. The observed plasticity is likely part of the central reorganization produ cing the multitude of sensory disturbances that surface following spinal co rd injury.