Objective: To study the peripheral and central neural involvements of acupoint "Taixi" (KI 3) by using Horseradish Peroxidase (HRP).
Methods: Ten male SD rats were used in the present study. 5 pL of 1% HRP was injected into the excavate site between the apex of medial malleolus and the Achilles tendon of the left hind foot, a corresponding site of acupoint "Taixi" (KI 3) in the human body. After 36 surviving hours, the rat's brain, spinal cord and dorsal root ganglia (DRG) of the lumbar segments (L) were dissected from the perfused experimental animals, and their tissue sections were examined with 3, 3', 5, 5' -tetramethyl-benzidine histochemistry for revealing HRP-labeling.
Results: All the HRP-labeling appeared ipsilaterally to the injection side. Numerous HRP-labeled neurons were detected in the DRGs of L4 - L6 segments with their number being L5> L4 >L6. A longitudinal column of HRP-labeled motoneurons was found in the dorsolateral and mediolateral portions of the spinal cord, distributing in the lamina IX from the caudal L4 to the rostral L6. Additionally, the transganglionic HRP-labeled central prolection axonal terminals were found to be dense in the central part of laminae I-II from L4 to the rostral L6, and to scatter in the central part of gracile nucleus.
Conclusion: HRP-labeled primary afferent and efferent innervating acupoint "Taixi" (KI 3) are DRGs of L4-L6, the dorsolateral and mediolateral motoneuron columns of L4-L6, and the centrally projecting axonal terminals of laminae I-II of the spinal cord and the gracile nucleus.