title: Cholinergic modulation of primary afferent glutamatergic transmission in rat medullary dorsal horn neurons.
abstract: Although muscarinic acetylcholine (mACh) receptors are expressed in trigeminal ganglia, it is still unknown whether mACh receptors modulate glutamatergic transmission from primary afferents onto medullary dorsal horn neurons. In this study, we have addressed the cholinergic modulation of primary afferent glutamatergic transmission using a conventional whole cell patch clamp technique. Glutamatergic excitatory postsynaptic currents (EPSCs) were evoked from primary afferents by electrical stimulation of trigeminal tract and monosynaptic EPSCs were recorded from medullary dorsal horn neurons of rat horizontal brain stem slices. Muscarine and ACh reversibly and concentration-dependently decreased the amplitude of glutamatergic EPSCs and increased the paired-pulse ratio. In addition, muscarine reduced the frequency of miniature EPSCs without affecting the current amplitude, suggesting that muscarine acts presynaptically to decrease the probability of glutamate release onto medullary dorsal horn neurons. The muscarine-induced decrease of glutamatergic EPSCs was significantly occluded by methoctramine or AF-DX116, M2 receptor antagonists, but not pirenzepine, J104129 and MT-3, selective M1, M3 and M4 receptor antagonists. The muscarine-induced decrease of glutamatergic EPSCs was highly dependent on the extracellular Ca2+ concentration. Physostigmine and clinically available acetylcholinesterase inhibitors, such as rivastigmine and donepezil, significantly shifted the concentration-inhibition relationship of ACh for glutamatergic EPSCs. These results suggest that muscarine acts on presynaptic M2 receptors to inhibit glutamatergic transmission by reducing the Ca2+ influx into primary afferent terminals, and that M2 receptor agonists and acetylcholinesterase inhibitors could be, at least, potential targets to reduce nociceptive transmission from orofacial tissues.
authors: Department of Pharmacology, School of Dentistry, Kyungpook National University, Daegu, Republic of Korea.
authors: Seok-Gwon
authors: SG
authors: Jeong
authors: Department of Pharmacology, School of Dentistry, Kyungpook National University, Daegu, Republic of Korea.
authors: In-Sun
authors: IS
authors: Choi
authors: Department of Pharmacology, School of Dentistry, Kyungpook National University, Daegu, Republic of Korea.
authors: Jin-Hwa
authors: JH
authors: Cho
authors: Department of Pharmacology, School of Dentistry, Kyungpook National University, Daegu, Republic of Korea; Brain Science & Engineering Institute, Kyungpook National University, Daegu 700-412, Republic of Korea. Electronic address: jis7619@mail.knu.ac.kr.
authors: Il-Sung
authors: IS
authors: Jang
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D018678:Cholinergic Agents / Q000494:pharmacology; D004347:Drug Interactions; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology*; D020671:Posterior Horn Cells / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043585:Receptor, Muscarinic M2 / Q000235:genetics / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D000779:Anesthetics, Local; D018678:Cholinergic Agents; D018683:Excitatory Amino Acid Agents; D018691:Excitatory Amino Acid Antagonists; D043585:Receptor, Muscarinic M2; D018698:Glutamic Acid; D013779:Tetrodotoxin; C056639:2-amino-5-phosphopentanoic acid; D014633:Valine; D000109:Acetylcholine
keywords: (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate; (αR)-α-cyclopentyl-α-hydroxy-N-[1-(4-methyl-3-pentenyl)-4-piperidinyl]benzeneacetamide fumarate; 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide; 11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one; 6-cyano-7-nitroquinoxaline-2,3-dione; 6-imino-3-(4-methoxyphenyl)-1(6H)-pyridazinebutanoic acid HBr; ACSF; ACh; AChE; AF-DX116; AM281; APV; CNQX; DL-2-amino-5-phosphonovaleric acid; DRG; EPSCs; J104129; Kolmogorov–Smirnov; K–S; Medullary dorsal horn; PPR; Pain; Patch clamp; Presynaptic mACh receptors; SEM; SR95531; TG; TTX; VDCCs; Win 55,212-2; [Ca(2+)](o); acetylcholine; acetylcholinesterase; artificial cerebrospinal fluid; dorsal root ganglion; excitatory postsynaptic currents; extracellular Ca(2+) concentration; mACh; mEPSCs; miniature excitatory postsynaptic currents; muscarinic acetylcholine; paired-pulse ratio; standard error of the mean; tetrodotoxin; trigeminal ganglion; voltage-dependent Ca(2+) channels