Innervated Properties of Acupuncture Points LI 4 and LR 3 in the Rat: Neural Pathway Tracing with Cholera Toxin Subunit B

Abstract

Objective: Increasing evidence from acupuncture research suggests that the nervous system corresponds closely with classical acupuncture points. The aim of this research was to provide neuroanatomical evidence for revealing the innervated properties of different acupuncture points through comparing the sensory and motor pathways associated with Hegu (LI 4) and Taichong (LR 3) in rat extremities. Materials and Methods: Cholera toxin subunit B (CTB) was injected into LI 4 and LR 3 in different rats, and CTB neural labeling was examined using fluorescent immunohistochemistry and observed under fluorescent microscopy in the corresponding areas from the peripheral nervous system to the central nervous system, including the dorsal root ganglia (DRG), spinal cord, and brainstem. Results: When LI 4 was injected with CTB, CTB-labeled sensory neurons ranged from C-5 to T-1 DRG, and their transganglionic axons terminated in the C-5 to C-8 spinal dorsal horn as far as the cuneate nucleus, while labeled motor neurons were located in the C-7 to T-1 spinal ventral horn. In contrast, similar neural labeling was observed for LR 3 CTB injection, with an orderly arrangement in the L-3 to L-5 DRG, L-3 to L-5 spinal dorsal horn, gracile nucleus, and L-4 to L-6 spinal ventral horn. Conclusions: The present results provide further evidence to aid understanding of the differential innervation of acupuncture points LI 4 and LR 3. This innervation establishes its connection with the nervous system in a distinct segmental and regional pattern through the spinal sensory and motor pathways.

Modulation of colonic function in irritable bowel syndrome rats by electroacupuncture at ST25 and the neurobiological links between ST25 and the colon

“…Then a double fluorescent neural tracing technique with Alexa Fluor 488 and 594 conjugates of cholera toxin subunit B (AF488/594-CTB) was used for figuring out the neuronal correlation between ST25 and the colon. Tao et al (1981) was a pioneer in applying nerve tracing techniques to acupuncture, and retrograde nerve tracing has been successfully used to study the neuroanatomical connections of acupoints–target organs ( Cui et al, 2015 , 2019 ; Xu et al, 2021 ; Zhang et al, 2021 ). By injecting different nerve tracers, sensory, sympathetic, and motor neurons associated with ST25 and the colon can be observed.…”

Correlated Sensory and Sympathetic Innervation Between the Acupoint BL23 and Kidney in the Rat

“…Through the injection of different neural tracers, sensory, sympathetic and motor neurons associated with BL23 and kidney can be observed. These two kinds of effective tools have been successfully applied in the field of acupuncture research (Xu et al, 2016 ; Wang et al, 2018b ; Cui J. J. et al, 2019 ). By taking their advantages, we expect not only to determine the innervated characteristics of acupoint BL23 and kidney individually but also to outline the neuronal correlation between them via the sensory and sympathetic pathways.…”

Comparison of Sensory and Motor Innervation Between the Acupoints LR3 and LR8 in the Rat With Regional Anatomy and Neural Tract Tracing

“…In order to reveal the differential innervation between LR3 and LR8 from the PNS to the CNS, their neural characteristics were systematically examined by the techniques of regional anatomy and neural tract tracing on the experimental rats. The two techniques have been used popularly in acupuncture research ( Cui et al, 2013a , b , 2019 ; Wu et al, 2015 ; Wang et al, 2018 ; Lee et al, 2019 ; Wang H. et al, 2019 ; Wang J. et al, 2019 ). Herein, regional anatomy was used to show the peripheral nerves under the regions of LR3 and LR8, and neural tract tracing was applied to trace the origin and termination of the sensory and motor innervation from both acupoints to the CNS.…”

“…Herein, regional anatomy was used to show the peripheral nerves under the regions of LR3 and LR8, and neural tract tracing was applied to trace the origin and termination of the sensory and motor innervation from both acupoints to the CNS. According to our previous studies, single cholera toxin subunit B (CTB) and dual Alexa Fluor 594/488 conjugated with CTB (AF594/488-CTB) were selected for neural tract tracing in this study ( Wang et al, 2018 ; Cui et al, 2019 ; Wang H. et al, 2019 ; Zhang et al, 2021 ). With the peripheral application, the single CTB is capable of retrogradely and transganglionically labeling the sensory and motor neurons and the sensory axon terminals ( Cui et al, 2013a , 2019 ; Wang et al, 2018 ).…”

“…According to our previous studies, single cholera toxin subunit B (CTB) and dual Alexa Fluor 594/488 conjugated with CTB (AF594/488-CTB) were selected for neural tract tracing in this study ( Wang et al, 2018 ; Cui et al, 2019 ; Wang H. et al, 2019 ; Zhang et al, 2021 ). With the peripheral application, the single CTB is capable of retrogradely and transganglionically labeling the sensory and motor neurons and the sensory axon terminals ( Cui et al, 2013a , 2019 ; Wang et al, 2018 ). Additionally, dual AF594/488-CTB are preferentially used in pair to retrogradely trace the sensory and motor neurons for identifying the neuronal correlation between the different acupoints or between the acupoint and its corresponding visceral organ ( Cui et al, 2013b ; Wang H. et al, 2019 ; Zhang et al, 2021 ).…”