[The expression of calcitonin gene-related peptide in the sensory and motor neurons associated with "Hegu" (LI 4) in the rat].

ABSTRACT

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 4 SD rats were used in the present study. After anesthesia, the rats received microinjection of 5 microL of Alexa Fluor 594 conjugated 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 gene-related 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) 5 to thoracic (T) 1 segments with a high concentration in C 7 DRG 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 6 to T 1 segments, with a high concentration at C 8 in which 100% motor neurons were shown to be CGRP-positive. CONCLUSION: Acupoint LI 4 is innervated by sensory neurons from DRGs of C 5 - T 1 and 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 4 induced therapeutic effects.