Properties of femoral venous afferent inputs and lumbosacral distribution of spinal evoked activity.

The present studies were done to determine details of the anatomical and physiological characteristics of femoral-saphenous venous afferent input to the lumbar spinal cord. Gross anatomical examination revealed that afferent bundles could be seen coursing from the saphenous nerve to the femoral-saphenous vein. Compound action potentials elicited by femoral-saphenous venous afferent stimulation were recorded from the femoral nerve and in dorsal rootlets of the 6th lumbar cord segment. The compound action potentials included activity correlated with that of fibers conducting impulses at the rate of 31 to 61 m/s. Lumbar cord dorsum potentials elicited by femoral-saphenous venous afferent stimulation were abolished by rhizotomy of the most caudal rootlets of the 6th lumbar cord segment. L6 was also the cord segment from which the largest amplitude cord dorsum negative potentials were recorded, while action potentials with large late positive waves were recorded from more caudal cord segments. These observations suggested that the L6 segment contained the largest number of spinal neurons responding to primary femoral-saphenous venous afferent input, and that input reached the more caudal segments via intersegmental connections. A proposed physiological role of these afferents is briefly described.