Study on the Central Neural Pathways Connecting the Brain and Peripheral Acupoints Using Neural Tracers

BACKGROUND: Acupuncture is widely used for therapeutic purposes, but the neural mechanisms underlying its effects are not fully understood. This study aims to investigate the neural projections from acupoints and subcutaneous (sham acupoints) sites to the central nervous system, using retrograde tracing technology, to clarify the specificity of acupuncture's neural pathways. METHODS: Adult C57BL/6J mice were injected with the retrograde tracer PRV-CAG-3 × mScarlet at seven acupoints (LI4, GV20, LI11, BL23, LR3, ST25, ST36) and their corresponding subcutaneous sites (sham acupoints). After 120 h, the brains were processed to assess viral expression and neural projections using histological analysis and imaging techniques. RESULTS: The results revealed differences in neural projections between the acupoint groups and their corresponding subcutaneous sites. Acupoints exhibited common neural projections to regions such as the primary motor cortex (M1), secondary motor cortex (M2), gigantocellular reticular nucleus (Gi), and ventrolateral periaqueductal gray (VLPAG), while subcutaneous sites showed more diffuse and less specific projections. CONCLUSIONS: Compared to subcutaneous injection sites (sham acupoints), acupoints exhibit common neural projections in the brain. In contrast to the more diffuse neural projection patterns observed in subcutaneous sites (sham acupoints), acupoints display more numerous and specific neural projections in the brain.