Different central manifestations in response to electroacupuncture at analgesic and nonanalgesic acupoints in rats: a manganese-enhanced functional magnetic resonance imaging study

Abstract

Acupuncture analgesia is an important issue in veterinary medicine. This study was designed to elucidate central modulation effects in response to electroacupuncture (EA) at different acupoints. Manganese-enhanced functional magnetic resonance imaging was performed in Sprague-Dawley rats after sham acupuncture, sham EA, or true EA at somatic acupoints. The acupoints were divided into 3 groups: group 1, analgesic acupoints commonly used for pain relief, such as Hegu (LI 4); group 2, nonanalgesic acupoints rarely used for analgesic effect such as Neiguan (PC 6); and group 3, acupoints occasionally used for analgesia, such as Zusanli (ST 36). Image acquisition was performed on a 1.5-T superconductive clinical scanner with a circular polarized extremity coil. The results showed that there was no neural activation caused by EA at a true acupoint with shallow needling and no electric current (sham acupuncture). When EA at a true acupoint was applied with true needling but no electric current (sham EA), there was only a slight increase in brain activity at the hypothalamus; when EA was applied at a true acupoint with true needling and an electric current (true EA), the primary response at the hypothalamus was enhanced. Also, there was a tendency for the early activation of pain-modulation areas to be prominent after EA at analgesic acupoints as compared with nonanalgesic acupoints. In conclusion, understanding the linkage between peripheral acupoint stimulation and central neural pathways provides not only an evidence-based approach for veterinary acupuncture but also a useful guide for clinical applications of acupuncture.

Figure 1. Experimental setup. Functional magnetic resonance imaging (fMRI) was performed at baseline and the indicated number of minutes after mannitol administration, MnCl₂ injection, electroacupuncture (EA), and the end of EA stimulation or removal of the needles. ECA — external carotid artery; ICA — internal carotid artery; CCA — common carotid artery.

Figure 2. Transverse images obtained by manganese-enhanced functional magnetic resonance imaging (fMRI) (Mn²⁺-fMRI) of the brain of rats at baseline (A) and 5, 10, and 20 min after infusion of MnCl₂ into the internal carotid artery (ICA). No electroacupuncture (EA) was done. Images were obtained at the level of the hypothalamus and thalamus. Nonspecific increases in signal intensity are apparent in the cortex (arrow) and in the hypothalamus (arrowhead).

Figure 3. Transverse images obtained by Mn²⁺-functional magnetic resonance imaging (fMRI) of the brain of rats 5 min after the start of acupuncture stimulation. A: Sham acupuncture (stimulation at a true acupoint [Hegu (LI 4)], with shallow needling and no electric current). B: Sham electroacupuncture (EA) (stimulation at Hegu with true needling but no electric current). C: True EA (stimulation at Hegu with true needling and an electric current). D: Control EA (stimulation at a control acupoint 2 mm from a true acupoint, with true needling and an electric current). Increased signal intensity is apparent in the hypothalamus (arrow) and in the thalamus (arrowhead).

Figure 4. Transverse images obtained by Mn²⁺-functional magnetic resonance imaging (fMRI) of the brain of rats 5 min after the start of electroacupuncture (EA) at Hegu (LI 4) in different animals (B–D), at the level of the hypothalamus and thalamus. As compared with sham EA (A), true EA results in an increase in signal intensity in the hypothalamus (arrowhead).

Figure 5. Transverse images obtained as with Figure 4 but at the level of the midbrain. As compared with sham electroacupuncture (EA) (A), true EA results in an increase in signal intensity in the periaqueduct grey (PAG) matter (arrowhead) and in the median raphe nucleus (MnR) (arrow).

Figure 6. Transverse images obtained by Mn²⁺-functional magnetic resonance imaging (fMRI) of the brain of rats at the level of the hypothalamus and thalamus (A and B) and the midbrain (C). Increased signal intensity 5 min after the start of electroacupuncture (EA) at Riyue (GB 24) is apparent in the sensory cortex (A, arrowhead) and in the hypothalamus (B, arrow) but not in the PAG and MnR regions (C).

Figure 7. Transverse images obtained by Mn²⁺-functional magnetic resonance imaging (fMRI) of the brain of rats at the level of the hypothalamus and thalamus 5 min after the start of electroacupuncture (EA) at Quchi (LI 11) (A) and Zhiyin (BL 67) (B) and 5 min after the end of EA or the removal of the needles from the Quchi (C) and Zhiyin (D) acupoints. Increased signal change is apparent in the hypothalamus, insula, and sensory cortex 5 min after the end of EA at Hegu (LI 4), whereas the signal changes are persistent in the hypothalamus (arrow) and thalamus (arrowhead) 5 min after the end of EA at Zhiyin.