Spread of the dorsal root potentials in lower lumbar, sacral and upper caudal spinal cord

Abstract

Spread of the dorsal root potentials (DRPs) along lower lumbar, sacral, and upper caudal segments of the cord has been studied in spinal cats. Ipsilateral DRPs produced by stimulation of L5 dorsal root with single volleys and recorded in consecutively more and more caudal segments gradually decrease and after passing 6 segments attain 47% of amplitude observed in L6 dorsal root. DRPs spreading cranially from Ca2 dorsal root along 6 segments decrease virtually to zero. Depolarizations spreading caudally show greater conduction velocity, are maintained during repetitive stimulation in larger number of segments and display larger occlusion than DRPs spreading cranially. These findings show the preponderance of depolarization spreading from lower lumbar cord to sacral and caudal segments over that produced in caudal parts of the cord and spreading cranially. The extent of cranial spread of DRPs, appearance of sudden increases in latency of DRPs and changes in effectiveness of stimulation in maintaining prolonged depolarization show correlations with neuronal arrangement of the substantia gelatinosa. This suggests that substantia gelatinosa subserves the spread of DRPs along the spinal cord.