Differential regulation of primary afferent input to spinal cord by muscarinic receptor subtypes delineated using knockout mice.
Stimulation of muscarinic acetylcholine receptors (mAChRs) inhibits nociceptive transmission at the spinal level. However, it is unclear how each mAChR subtype regulates excitatory synaptic input from primary afferents. Here we examined excitatory postsynaptic currents (EPSCs) of dorsal horn neurons evoked by dorsal root stimulation in spinal cord slices from wild-type and mAChR subtype knock-out (KO) mice. In wild-type mice, mAChR activation with oxotremorine-M decreased the amplitude of monosynaptic EPSCs in ∼67% of neurons but increased it in ∼10% of neurons. The inhibitory effect of oxotremorine-M was attenuated by the M2/M4 antagonist himbacine in the majority of neurons, and the remaining inhibition was abolished by group II/III metabotropic glutamate receptor (mGluR) antagonists in wild-type mice. In M2/M4 double-KO mice, oxotremorine-M inhibited monosynaptic EPSCs in significantly fewer neurons (∼26%) and increased EPSCs in significantly more neurons (33%) compared with wild-type mice. Blocking group II/III mGluRs eliminated the inhibitory effect of oxotremorine-M in M2/M4 double-KO mice. In M2 single-KO and M4 single-KO mice, himbacine still significantly reduced the inhibitory effect of oxotremorine-M. However, the inhibitory and potentiating effects of oxotremorine-M on EPSCs in M3 single-KO and M1/M3 double-KO mice were similar to those in wild-type mice. In M5 single-KO mice, oxotremorine-M failed to potentiate evoked EPSCs, and its inhibitory effect was abolished by himbacine. These findings indicate that activation of presynaptic M2 and M4 subtypes reduces glutamate release from primary afferents. Activation of the M5 subtype either directly increases primary afferent input or inhibits it through indirectly stimulating group II/III mGluRs.
From the Center for Neuroscience and Pain Research, Department of Anesthesiology and Perioperative Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 and.
Shao-Rui
SR
Chen
From the Center for Neuroscience and Pain Research, Department of Anesthesiology and Perioperative Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 and.
Hong
H
Chen
From the Center for Neuroscience and Pain Research, Department of Anesthesiology and Perioperative Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 and.
Wei-Xiu
WX
Yuan
the Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
Jürgen
J
Wess
From the Center for Neuroscience and Pain Research, Department of Anesthesiology and Perioperative Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 and huilinpan@mdanderson.org.
Hui-Lin
HL
Pan
D000818:Animals; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D018698:Glutamic Acid / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000494:pharmacology; D020671:Posterior Horn Cells / Q000166:cytology* / Q000187:drug effects; D011976:Receptors, Muscarinic / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D013126:Spinal Nerve Roots / Q000166:cytology
D011976:Receptors, Muscarinic; D018698:Glutamic Acid; D010095:Oxotremorine; C042743:oxotremorine M
Acetylcholine; Acetylcholinesterase; Cholinergic Receptor; Gene Knockout; Glutamate; Muscarinic; Neurons; Pain; Spinal Cord; Synaptic Plasticity