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 5μL of 1% CTB solution was injected into the front central part of hind foot plantar(corresponding to the KI 1region in the human body)using a Hamilton microsyringe.After 3survival 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 3-5segments(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 3to L 6with a higher concentration at L 5.In addition

transganglionic axonal projections were found to situate in the medial part of laminaeⅢ-Ⅳfrom L 3to L 5

as far as in the gracile nucleus.Conclusion Acupoint KI 1area is innervated by sensory neurons in L 3-L 5DRGs 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 laminaeⅢ-Ⅳ of L 3-L 5and gracile nucleus

respectively.