Objective: To observe the distribution of neurons and their axonal projection associated with "Yongquan" (KI 1) area by neural tracing technique with cholera toxin subunit B (CTB).
Methods: A total of 5 microL of 1% CTB solution was injected into the front central part of hind foot plantar (corresponding to the KI 1 region in the human body) using a Hamilton microsyringe. After 3 survival days, the rats were deeply anesthetized and transcardically perfused for collecting the dorsal root ganglia (DRGs), spinal cord and brain tissues. Following fixing in 4% paraforldehyde containing phosphate buffer solution (PBS) and incubation in PBS containing 25% glucose solution, the aforementioned tissues were sectioned to be stained with immunofluorescence or immunohistochemistry for revealing the labeled sensory neurons and their tansganglionic projection and motor neurons.
Results: All the labeled neurons (sensory and motor neurons) and transganglionic axonal projection appeared ipsilaterally to the injection side. The labeled sensory neurons were located in the DRGs of lumbar 3-5 segments (L 3-L 5) with a higher concentration at L 4, while motor neurons distributed in the dorsolateral portion of spinal ventral horn from L 3 to L 6 with a higher concentration at L 5. In addition, transganglionic axonal projections were found to situate in the medial part of laminae III - IV from L 3 to L 5, as far as in the gracile nucleus.
Conclusion: Acupoint KI 1 area is innervated by sensory neurons in L 3-L 5 DRGs and motor neurons from the dorsolateral ventral horns of L 3-L 6. The axonal projection of the primary sensory neurons distributes in the medial part of laminae III - IV of L 3-L 5 and gracile nucleus, respectively.