Neuroanatomical characteristics of deep and superficial needling using LI11 as an example

Abstract

Objectives: To compare the neuroanatomical characteristics of the deep and superficial tissues at acupuncture point LI11 using a neural tracing technique, in order to examine the neural basis of potential differences between deep and superficial needling techniques.

Methods: In order to mimic the situations of the deep and superficial needling, the retrograde neural tracer Alexa Fluor 488 conjugate of cholera toxin subunit B (AF488-CTB) was injected into the muscle or subcutaneous tissue, respectively, at acupuncture point LI11 in eight rats (n=4 each). Three days following injection, the distribution of motor and sensory neurons labelled with AF488-CTB was examined in the spinal cord and dorsal root ganglia (DRG) under a fluorescent microscope.

Results: For both types of injection, labelled motor and sensory neurons were distributed on the side ipsilateral to the injection in the spinal cord and DRG between spinal levels C5 and T1. The number of labelled motor neurons following intramuscular injection was significantly higher than subcutaneous injection. By contrast, the number of labelled sensory neurons following subcutaneous injection was significantly higher in number and extended over a greater number of spinal segments compared to intramuscular injection.

Conclusions: These data indicate that the motor and sensory innervation of muscle and subcutaneous tissue beneath LI11 differ, and suggest that acupuncture signals induced by deep and superficial needling stimulation may be transmitted through different neural pathways.

Keywords: ACUPUNCTURE.

Figure 1

Distribution of the retrograde neural tracer Alexa Fluor 488 conjugate of cholera toxin subunit B (AF488-CTB) in local tissues from the region of acupuncture point LI11. (A) After intramuscular injection, AF488-CTB was limited to a relatively small area within the muscle tissue. (B) After subcutaneous injection, AF488-CTB spread widely in subcutaneous tissue.

Figure 2

Labelled motor neurons in representative transverse sections of the ventral horn of C8 spinal cord (at two different levels of magnification) from eight experimental rats 3 days following intramuscular (A, A1) or subcutaneous (B, B1) injections of the retrograde neural tracer Alexa Fluor 488 conjugate of cholera toxin subunit B (AF488-CTB) at acupuncture point LI11 (n=4 each). The same scale bars apply to A and B and A1 and B1, respectively.

Figure 3

Labelled sensory neurons in representative sagittal sections of the C8 dorsal root ganglia (DRG) from eight experimental rats 3 days following intramuscular (A) or subcutaneous (B) injections of the retrograde neural tracer Alexa Fluor 488 conjugate of cholera toxin subunit B (AF488-CTB) at acupuncture point of LI11 (n=4 each). The same scale bar applies to A and B.

Figure 4

Average number of labelled sensory neurons at each spinal level from C5 to T1 in eight experimental rats 3 days following intramuscular (blue) or subcutaneous (purple) injection of the retrograde neural tracer Alexa Fluor 488 conjugate of cholera toxin subunit B (AF488-CTB) at acupuncture point of LI11 (n=4 each). Data are expressed as mean±SD.

Figure 5

A series of line drawings through spinal levels C5 to T1 illustrating the dorsal root ganglia (DRG) and transverse spinal cord showing the general distribution of sensory and motor neurons labelled with the retrograde neural tracer Alexa Fluor 488 conjugate of cholera toxin subunit B (AF488-CTB) 3 days following intramuscular injection (left side) or subcutaneous injection (right side) at acupuncture point LI11 in the rat (n=4 each). The black dots in the DRG and spinal cord represent the labelled sensory and motor neurons respectively, and the numbers of dots reflect the relative quantities of labelled neurons between rats receiving intramuscular and subcutaneous injection at each spinal level.