Neural mechanism of acupuncture-modulated gastric motility

Abstract

Aim: To investigate the acupuncture-modulated gastric motility and its underlying neural mechanism.

Methods: Intragastric pressure and/or waves of gastric contraction in rats were recorded by intrapyloric balloon and changes of gastric motility induced by acupuncture stimulation were compared with the background activity before any stimulation. Gastro-vagal or splanchnic-sympathetic nerves were recorded or cut respectively for investigating the involvement of autonomic nerve pathways. Spinalization experiment was also performed.

Results: Acupuncture-stimulation by exciting A delta and/or C afferent fibers, could only modulate gastric motility. Acupuncture-stimulation on fore- and hind-limbs evoked a moderate gastric motility followed by increased vagus discharges with unchanged sympathetic activity, while the same stimulus to the acupoints in abdomen resulted in reversed effects on gastric motility and autonomic nervous activities. The inhibitory gastric response was completely abolished by splanchnic denervation, but the facilitative gastric response to stimulation of acupoints in limbs was not influenced, which was opposite to the effect when vagotomy was performed. The similar depressive effects were produced by the stimulation at the acupoints homo-segmental to the gastric innervation in the animals with or without spinalization. However, the facilitation induced by the stimulation at the acupoints hetero-segmental to the gastric innervation was not observed in the spinalized animals.

Conclusion: Facilitative effects of stimulating hetero-segmental acupoints are involved in the intact preparation of vagal nerves and spinal cord, while the inhibitory response induced by stimulating homo-segmental acupoints is involved in the intact preparation of sympathetic nerves. Only the acupuncture-stimulation with intensity over the threshold of A delta and/or C afferent fibers can markedly modulate gastrointestinal motility.

Figure 1

Gastric motility response to electro-acupuncture stimulation with different intensities. Gastric motility was recorded for 90 s, of which the first 20 s was the duration of spontaneous background of gastric activity, 21-50 s was the period of acupuncture stimulation at acupoints, poststimuli activity was recorded for 51-90 s. Dash line represents located abdominal acupoints.

Figure 2

Quantitative analysis of gastric motility in strength-dependent response to electro-acu puncture-stimulation applied to the acupoints on different parts of body. “< Aδ“: the intensity of the stimulation less than the threshold for activation of Aδ-fiber; “> Aδ < C”: the intensity of the stimulation over the threshold for activation of Aδ-fiber, but less than the threshold for activation of C-fiber; “> C”: the intensity of the stimulation over the threshold for activation of C-fiber.

Figure 3

Gastric motility and autonomic nerve responses to acupuncture stimulation at different acupoints. In each acupoint stimulus, gastric motility (GM), activities of gastric vagal (vagus) and postganglionic sympathetic nerve branches to the stomach (symp), were simultaneously recorded.

Figure 4

Effect of acupuncture stimulation on gastric motility in animals with intact autonomic nervous system, after sympathectomy of bilateral splanchnic nerves just beneath the diaphragm but intact vagi and bilateral subdiaphragmatic vagotomy but intact sympathetic nerve.

Figure 5

Analysis of the changes in gastric motility induced by acupuncture stimulation in rats after bilateral sympathectomy (A) of splanchnic nerves and vagotomy (B), respectively. ^aP < 0.05, ^bP < 0.01 and ^dP < 0.001 vs animals with intact autonomic nervous system.

Figure 6

Effects of acupuncture stimulation involving the supraspinal circuit on gastric motility in normal (A) and spinalized (B) rats.

Figure 7

Effects of acupuncture stimulation at different acupoints on the regulation of gastric motility in normal and spinalized rats. Triangle-lines represent the pre-spinalized effects and square-lines indicate the post-spinalized effects. ^aP < 0.05, ^bP < 0.01 and ^dP < 0.001 vs the control gastric motility of pre-spinalization.