Development and Characterization of the Rat Paraplegia Model
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Paralysis in the lower extremities following trauma, extrinsic compression, profound shock, and certain surgical procedures in the human is an important problem. In the past, research has been restricted to a rabbit spinal cord ischemia model which has the disadvantage of a poorly defined range for grading neurologic deficit. The goal of this study was to develop a model of paraplegia in the more neurologically versatile rat. Eight surgical interventions were attempted before achieving a permanent paraplegia which lasted beyond a temporary occlusion period. The successful surgical method involved a thoracotomy with division of the right internal thoracic artery followed by a 15 minute occlusion of the thoracic aorta between the left common carotid and left subclavian arteries. An experimenter-performed neurologic score was developed to grade fine differences in degrees of deficit. Three separate occlusion periods (10, 15, and 20 minutes) were tested and it was determined that a 15 minute occlusion period produced an intermediate degree of deficit based on the neurologic deficit scale. In addition to the neurologic deficit scale, a computerized activity monitor was adapted to characterize the range of neurologic deficit produced. Normal rats were tested in both a divided and an undivided computerized activity monitor to determine baseline activity levels and to define the effects of habituation. Rats were more active in undivided cages and, therefore, greater ranges of activity could be separated following paraplegia. Based on these results, experimental rats, after receiving control injections of saline, underwent 15 minute occlusion periods followed by neurologic deficit scoring (1, 4, 18, 24 hours postocclusion) and computerized activity monitoring in an undivided cage (1 and 18 hours postocclusion). It is concluded that: 1) Paraplegia is reliably and reproducibly achieved in this rat model, 2) Because of the more extensive behavioral repertoire of the laboratory rat when compared to other models of spinal ischemia (rabbit), more endpoints can be monitored and more subtle behavioral deficits discerned, 3) Computerized activity monitoring can distinguish varying degrees of neurologic deficit in the rat paraplegia model, but further refinement is required.