title: Low concentrations of pyridostigmine prevent soman-induced inhibition of GABAergic transmission in the central nervous system: involvement of muscarinic receptors.
abstract: This study was designed to investigate the effects of the cholinesterase inhibitors soman and pyridostigmine bromide (PB) on synaptic transmission in the CA1 field of rat hippocampal slices. Soman (1-100 nM, 10-15 min) decreased the amplitude of GABAergic postsynaptic currents (IPSCs) evoked by stimulation of Schaffer collaterals and recorded from CA1 pyramidal neurons. It also decreased the amplitude and frequency of spontaneous IPSCs recorded from pyramidal neurons. Whereas the maximal effect of soman on evoked GABAergic transmission was observed at 10 nM, full cholinesterase inhibition was induced by 1 nM soman. After 10-15-min exposure of hippocampal slices to 100 nM PB, GABAergic transmission was facilitated and cholinesterase activity was not significantly affected. At nanomolar concentrations, soman and PB have no direct effect on GABA(A) receptors. The effects of soman and PB on GABAergic transmission were inhibited by the m2 receptor antagonist 11-[[[2-diethylamino-O-methyl]-1-piperidinyl] acetyl]-5,11-dihydrol-6H-pyridol[2,3-b][1,4]benzodiazepine-6- one (1 nM) and the m3 receptor antagonist 4-diphenylacetoxy-N-methyl-piperidine (100 nM), respectively, and by the nonselective muscarinic receptor antagonist atropine (1 microM). Thus, changes in GABAergic transmission are likely to result from direct interactions of soman and PB with m2 and m3 receptors, respectively, located on GABAergic fibers/neurons synapsing onto the neurons under study. Although the effects of 1 nM soman and 100 nM PB were diametrically opposed, they only canceled one another when PB was applied to the neurons before soman. Therefore, PB, acting via m3 receptors, can effectively counteract effects arising from the interactions of soman with m2 receptors in the brain.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
authors.forename: Máriton D
authors.initials: MD
authors.lastname: Santos
authors.forename: Edna F R
authors.initials: EF
authors.lastname: Pereira
authors.forename: Yasco
authors.initials: Y
authors.lastname: Aracava
authors.forename: Newton G
authors.initials: NG
authors.lastname: Castro
authors.forename: William P
authors.initials: WP
authors.lastname: Fawcett
authors.forename: William R
authors.initials: WR
authors.lastname: Randall
authors.forename: Edson X
authors.initials: EX
authors.lastname: Albuquerque
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002490:Central Nervous System / Q000187:drug effects*; D002800:Cholinesterase Inhibitors / Q000494:pharmacology*; D002802:Cholinesterases / Q000378:metabolism; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000494:pharmacology; D010890:Pirenzepine / Q000031:analogs & derivatives* / Q000494:pharmacology; D017966:Pyramidal Cells / Q000187:drug effects; D011729:Pyridostigmine Bromide / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000187:drug effects*; D011978:Receptors, Nicotinic / Q000187:drug effects; D012999:Soman / Q000037:antagonists & inhibitors* / Q000633:toxicity; D009435:Synaptic Transmission / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
chemical_list: D002800:Cholinesterase Inhibitors; D018727:Muscarinic Antagonists; D010880:Piperidines; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D010890:Pirenzepine; D005680:gamma-Aminobutyric Acid; D001285:Atropine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D012999:Soman; D002802:Cholinesterases; D011729:Pyridostigmine Bromide; C048593:otenzepad