Objective To investigate the chemical expression of the primary sensory and motor neurons associated with "Hegu"(LI 4)area by using neural tracing and fluorescent immunohistochemical techniques.Methods A total of 4SD rats were used in the present study.After anesthesia

the rats received microinjection of 5μL of Alexa Fluor 594conjugated cholera toxin subunit B(AF 594-CTB)into the right"Hegu"(LI 4)area for observing the distribution of the related primary sensory neurons in dorsal root ganglia(DRGs)and motor neurons in the spinal cord(C 1-C 5).Three days after the microinjection

the rats were anesthetized and transcardiacally perfused with 4% paraformaldehyde

followed by routine section of the DRGs and spinal cord tissues.The labeled neurons were observed by light microscope and their chemical characteristics determined by calcitonin generelated peptide(CGRP)fluorescent immunohistochemical method.Results All the AF 594-CTB labeled neurons in DRGs and spinal cord were located on the side of the tracer injection.The labeled sensory neurons distributed in DRGs of cervical(C)5to thoracic(T)1segments with a high concentration in C 7DRG in which 73.5%sensory neurons were shown to be CGRP-positive. The labeled motor neurons were found to be in the dorsolateral region of the spinal anterior horns from C 6to T 1segments

with a high concentration at C 8in which 100% motor neurons were shown to be CGRP-positive.Conclusion Acupoint LI 4is innervated by sensory neurons from DRGs of C 5-T 1and motor neurons from anterior horns of the same segmental spinal cord in rats. Among them

73.5% of the sensory neurons and 100% of the motor neurons are CGRP-positive

suggesting an involvement of CGRP in acupuncture stimulation-LI 4induced therapeutic effects.