Abstract: Objective To investigate the role of muscarinic cholinergic receptor (mAChR) subtypes in the regulation of
glutamatergic input to the spinal dorsal horn neurons and the possible mechanism. Methods Whole-cell voltage-clamp
recordings on acute spinal slice was utilized to investigate the effect of activation of mAChRs and blockade of M2/M4 subtypes
on glutamatergic synaptic transmission in rat spinal dorsal horn neurons. Results The nonselective mAChRs agonist
oxotremorine-M concentration-dependently decreased the amplitude of monosynaptic and polysynaptic evoked
glutamate-mediated excitatory postsynaptic currents (eEPSCs) in most of the neurons. The M2/M4 antagonist himbacine
completely blocked the inhibitory effect of oxotremorine-M in 92.3% of monosynaptic and 75% of polysynaptic neurons in the
spinal cord slices. In the remaining 16% neurons, himbacine partially blocked the inhibitory effect of oxotremorine-M.
Conclusions Activation of mAChRs in the spinal cord attenuates synaptic glutamate release to the dorsal horn neurons mainly
through M2 and M4 receptor subtypes, indicating that a presynaptic inhibition in the spinal cord may be involved in the
regulation of nociception by the cholinergic system and mAChRs.