Abstract

This study was performed to determine whether spinal cholinergic systems mediate the relieving effects of electroacupuncture (EA) on cold and warm allodynia in a rat model of neuropathic pain. For neuropathic surgery, the right superior caudal trunk was resected at the level between the S1 and S2 spinal nerves innervating the tail. Two weeks after the injury, the intrathecal (i.t.) catheter was implanted. Five days after the catheterization, the rats were injected with atropine (non-selective muscarinic antagonist, 30 μg), mecamylamine (non-selective nicotinic antagonist, 50 μg), pirenzepine (M ₁ muscarinic antagonist, 10 μg), methoctramine (M₂ antagonist, 10 μg) or 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) (M₃ antagonist, 10 μg). Ten minutes after the injection, EA was applied to the ST36 acupoint for 30 min. The cold and warm allodynia were assessed by the tail immersion test [i.e., immersing the tail in cold (4°C) or warm (40°C) water and measuring the latency of an abrupt tail movement] before and after the treatments. The i.t. atropine, but not mecamylamine, blocked the relieving effects of EA on cold and warm allodynia. Furthermore, i.t. pirenzepine attenuated the antiallodynic effects of EA, whereas methoctramine and 4-DAMP did not. These results suggest that spinal muscarinic receptors, especially M₁ subtype, mediate the EA-induced antiallodynia in neuropathic rats. © 2009 The Physiological Society of Japan and Springer.

Author keywords

Allodynia; Cholinergic; Electroacupuncture; Muscarinic; Neuropathic pain; Spinal cord

Indexed keywords

EMTREE drug terms: 4 diphenylacetoxy 1 methylpiperidine; atropine; mecamylamine; methoctramine; pirenzepine

EMTREE medical terms: allodynia; animal experiment; animal model; article; behavior; catheterization; cholinergic system; controlled study; electroacupuncture; male; neuropathic pain; nonhuman; rat; spinal nerve; tail; temperature sensitivity; water immersion

MeSH: Animals; Atropine; Cholinergic Agents; Cholinergic Fibers; Cold Temperature; Diamines; Disease Models, Animal; Electroacupuncture; Hot Temperature; Hyperesthesia; Male; Mecamylamine; Neuralgia; Pain Threshold; Piperidines; Pirenzepine; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M1; Spinal Nerves
Medline is the source for the MeSH terms of this document.

Chemicals and CAS Registry Numbers: 4 diphenylacetoxy 1 methylpiperidine, 1952-15-4; atropine, 51-55-8, 55-48-1; mecamylamine, 60-40-2, 826-39-1; methoctramine, 104807-46-7; pirenzepine, 28797-61-7, 29868-97-1;4-diphenylacetoxy-1,1-dimethylpiperidinium, 81405-11-0; Atropine, 51-55-8; Cholinergic Agents; Diamines; Mecamylamine, 60-40-2; Piperidines; Pirenzepine, 28797-61-7; Receptor, Muscarinic M1; methoctramine, 104807-46-7