title: Acetylcholinesterase inhibition reveals endogenous nicotinic modulation of glutamate inputs to CA1 stratum radiatum interneurons in hippocampal slices.
abstract: The involvement of brain nicotinic acetylcholine receptors (nAChRs) in the neurotoxicological effects of soman, a potent acetylcholinesterase (AChE) inhibitor and a chemical warfare agent, is not clear. This is partly due to a poor understanding of the role of AChE in brain nAChR-mediated functions. To test the hypothesis that AChE inhibition builds sufficient acetylcholine (ACh) in the brain and facilitates nAChR-dependent glutamate transmission, we used whole-cell patch-clamp technique to record spontaneous glutamate excitatory postsynaptic currents (EPSCs) from CA1 stratum radiatum interneurons (SRI) in hippocampal slices. First, the frequency, amplitude and kinetics of EPSCs recorded from slices of control guinea pigs were compared to those recorded from slices of guinea pigs after a single injection of the irreversible AChE inhibitor soman (25.2μg/kg, s.c.). Second, EPSCs were recorded from rat hippocampal slices before and after their superfusion with the reversible AChE inhibitor donepezil (100nM). The frequency of EPSCs was significantly higher in slices taken from guinea pigs 24h but not 7 days after the soman injection than in slices from control animals. In 52% of the rat hippocampal slices tested, bath application of donepezil increased the frequency of EPSCs. Further, exposure to donepezil increased both burst-like and large-amplitude EPSCs, and increased the proportion of short (20-100ms) inter-event intervals. Donepezil's effects were suppressed significantly in presence of 10μM mecamylamine or 10nM methyllycaconitine. These results support the concept that AChE inhibition is able to recruit nAChR-dependent glutamate transmission in the hippocampus and such a mechanism can contribute to the acute neurotoxicological actions of soman.
authors.affiliation: Division of Translational Toxicology, Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, United States.
authors.forename: Manickavasagom
authors.initials: M
authors.lastname: Alkondon
authors.forename: Edson X
authors.initials: EX
authors.lastname: Albuquerque
authors.forename: Edna F R
authors.initials: EF
authors.lastname: Pereira
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D056547:CA1 Region, Hippocampal / Q000166:cytology*; D002800:Cholinesterase Inhibitors / Q000494:pharmacology*; D000077265:Donepezil; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D018698:Glutamic Acid / Q000378:metabolism*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007189:Indans / Q000494:pharmacology; D007395:Interneurons / Q000187:drug effects*; D007928:Lethal Dose 50; D008297:Male; D008464:Mecamylamine / Q000494:pharmacology; D009538:Nicotine / Q000378:metabolism*; D018733:Nicotinic Antagonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000494:pharmacology; D051381:Rats; D012999:Soman / Q000494:pharmacology
chemical_list: D002800:Cholinesterase Inhibitors; D018691:Excitatory Amino Acid Antagonists; D007189:Indans; D018733:Nicotinic Antagonists; D010880:Piperidines; D018698:Glutamic Acid; D008464:Mecamylamine; D009538:Nicotine; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000077265:Donepezil; D012999:Soman; D000109:Acetylcholine