Increased [Met]enkephalin and decreased substance P in spinal cord following thermal injury to one limb

Abstract

Thermal injury to one hind limb of rats was induced by immersion into water at 62 degrees C. Both a mild (15 s) or severe (30 s) lesion caused inflammation of the limb when observed 24 h later; but at this time the animals used the injured limb when they walked. Animals with a severe lesion of the injured limb subsequently withdrew it from use when walking. Limb withdrawal did not occur following a mild lesion. At 24 h following the lesion, lumbar spinal cord levels of [Met]enkephalin, as measured by radioimmunoassay, were elevated (70%) bilaterally in both hemisegments, ipsi- and contralateral to the lesion. At seven days following either mild or severe hind limb lesion [Met]enkephalin levels were elevated only in the ipsilateral lumbar hemisegment. At that time no changes in thoracic [Met]enkephalin levels were observed. Substance P levels were decreased (20-25%) bilaterally in the lumbar cord 24 h following a severe limb lesion, but no change was observed at seven days in any cord segment following a mild or severe lesion. Changes in spinal cord [Met]enkephalin content occur in response to thermal injury to one hind limb. However, the changes do not appear to be related to the withdrawal of the damaged limb from use following a severe lesion. Peptide changes in the spinal cord may reflect pain or injury to the damaged limb following a thermal lesion. In contrast, limb withdrawal may be a physiological rest mechanism related to altered basal ganglia peptide function.