Peripheral muscarinic receptors mediate the anti-inflammatory effects of auricular acupuncture.
BACKGROUND
The cholinergic and opioid systems play important roles in modulating inflammation. This study tests whether auricular acupuncture (AA) produces anti-inflammatory effects via opioid and peripheral cholinergic receptors in a rat model.


METHODS
Rats were anesthetized with chloral hydrate and inflammation was induced by intraplantar injection of carrageenan. Electroacupuncture was performed at auricular points bilaterally. The severity of inflammation was assessed using changes in paw volume and thermal and mechanical pain thresholds of the rats during recovery from anesthesia.


RESULTS
Electroacupuncture at selected auricular acupoints significantly reduced paw edema and mechanical hyperalgesia, with no significant effect on thermal hyperalgesia. The anti-edematous and analgesic effects of AA were abolished by blockade of peripheral cholinergic muscarinic receptors with methyl atropine. Blockade of local muscarinic receptors at the inflamed site with a small dose of atropine also antagonized the anti-edematous effect of AA. By contrast, systemic opioid receptor blockade with naloxone did not antagonize the anti-inflammatory effects of AA.


CONCLUSIONS
This study discovers a role of peripheral muscarinic receptors in mediating the anti-inflammatory effects of AA. The cholinergic muscarinic mechanism appears to be more important than the opioid mechanism in the anti-inflammatory action of AA.
School of Chinese Medicine, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China. spzhang@hkbu.edu.hk.
Wai Yeung
WY
Chung
Hong Qi
HQ
Zhang
Shi Ping
SP
Zhang
Brain Res Bull. 2004 Mar 15;63(2):99-103
15130698
Anesth Analg. 2008 Feb;106(2):602-10
18227322
J Burn Care Rehabil. 1990 Jul-Aug;11(4):322-9
2205609
Acupunct Electrother Res. 1999;24(3-4):169-79
10768414
Braz J Med Biol Res. 2004 Mar;37(3):391-9
15060709
Brain Res Bull. 2004 Jan 15;62(4):327-34
14709347
J Neurosci. 2002 Jun 15;22(12):RC229
12045234
Neurosci Lett. 2004 May 6;361(1-3):258-61
15135942
Brain Res. 2005 Sep 28;1057(1-2):181-5
16139820
Fed Proc. 1987 Jan;46(1):118-26
3100339
Brain Res. 1992 Apr 10;577(1):80-91
1521149
J Auton Nerv Syst. 2000 Mar 15;79(2-3):93-8
10699639
Neuroscience. 2008 Aug 13;155(2):463-8
18606213
Neurosci Lett. 1998 Jan 30;241(2-3):79-82
9507925
J Auton Nerv Syst. 1995 Jan 20;51(1):27-35
7722213
Somatosens Mot Res. 1994;11(1):65-8
8017145
J Pain Symptom Manage. 1991 Feb;6(2):73-83
2007795
Neuroreport. 2001 Aug 8;12(11):2457-60
11496129
J Clin Oncol. 2003 Nov 15;21(22):4120-6
14615440
Anat Anz. 1991;173(2):107-12
1772130
Anesth Analg. 2004 May;98(5):1359-64, table of contents
15105215
Auton Neurosci. 2008 Feb 29;138(1-2):50-6
18068545
Auton Neurosci. 2000 Dec 20;85(1-3):141-7
11189021
Naunyn Schmiedebergs Arch Pharmacol. 1988 Jan;337(1):24-8
2897083
Am J Chin Med. 1991;19(3-4):199-205
1767791
Pain. 2004 Jan;107(1-2):22-32
14715385
Brain Res. 1991 May 17;549(1):36-46
1893251
Pain. 2002 Oct;99(3):525-535
12406529
Pain. 1983 Jun;16(2):109-110
6877845
Eur J Pharmacol. 1995 Sep 25;284(3):321-5
8666015
J Clin Invest. 2007 Feb;117(2):289-96
17273548
Anesth Analg. 2003 Nov;97(5):1469-1473
14570667
Lancet. 1979 Aug 25;2(8139):380-3
89447
Inflammation. 1994 Jun;18(3):285-92
7522223
Clin Anat. 2002 Jan;15(1):35-7
11835542
Pain. 2005 Apr;114(3):320-327
15777857