Opposing functions of spinal M2, M3, and M4 receptor subtypes in regulation of GABAergic inputs to dorsal horn neurons revealed by muscarinic receptor knockout mice.
Spinal muscarinic acetylcholine receptors (mAChRs) play an important role in the regulation of nociception. To determine the role of individual mAChR subtypes in control of synaptic GABA release, spontaneous inhibitory postsynaptic currents (sIPSCs) and miniature IPSCs (mIPSCs) were recorded in lamina II neurons using whole-cell recordings in spinal cord slices of wild-type and mAChR subtype knockout (KO) mice. The mAChR agonist oxotremorine-M (3-10 microM) dose-dependently decreased the frequency of GABAergic sIPSCs and mIPSCs in wild-type mice. However, in the presence of the M2 and M4 subtype-preferring antagonist himbacine, oxotremorine-M caused a large increase in the sIPSC frequency. In M3 KO and M1/M3 double-KO mice, oxotremorine-M produced a consistent decrease in the frequency of sIPSCs, and this effect was abolished by himbacine. We were surprised to find that in M2/M4 double-KO mice, oxotremorine-M consistently increased the frequency of sIPSCs and mIPSCs in all neurons tested, and this effect was completely abolished by 4-diphenylacetoxy-N-methylpiperidine methiodide, an M3 subtype-preferring antagonist. In M2 or M4 single-KO mice, oxotremorine-M produced a variable effect on sIPSCs; it increased the frequency of sIPSCs in some cells but decreased the sIPSC frequency in other neurons. Taken together, these data strongly suggest that activation of the M3 subtype increases synaptic GABA release in the spinal dorsal horn of mice. In contrast, stimulation of presynaptic M2 and M4 subtypes predominantly attenuates GABAergic inputs to dorsal horn neurons in mice, an action that is opposite to the role of M2 and M4 subtypes in the spinal cord of rats.
Zhang
Hong-Mei
HM
Department of Anesthesiology, Pennsylvania State University College of Medicine, Milton S. Hershey Medical Center, Hershey, USA.
Chen
Shao-Rui
SR
Matsui
Minoru
M
Gautam
Dinesh
D
Wess
Jürgen
J
Pan
Hui-Lin
HL
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D004594:Electrophysiology; D005663:Furans / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D020671:Posterior Horn Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D043585:Receptor, Muscarinic M2 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D043587:Receptor, Muscarinic M3 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D043588:Receptor, Muscarinic M4 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D000470:Alkaloids; D005663:Furans; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D009281:Naphthalenes; D010880:Piperidines; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D043588:Receptor, Muscarinic M4; D005680:gamma-Aminobutyric Acid; D010095:Oxotremorine; C042743:oxotremorine M; C048172:himbacine