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METHODS article

Front. Drug Discov.
Sec. Technologies and Strategies to Enable Drug Discovery
Volume 4 - 2024 | doi: 10.3389/fddsv.2024.1393964

An anesthetized rat assay for evaluating the effects of organophosphate-based compounds and countermeasures on intracranial EEG and respiratory rate

Provisionally accepted
Jeffrey S. Thinschmidt Jeffrey S. Thinschmidt 1James D. Talton James D. Talton 2Scott W. Harden Scott W. Harden 1Charles J. Frazier Charles J. Frazier 1*
  • 1 University of Florida, Gainesville, Florida, United States
  • 2 Alchem Laboratories (United States), Alachua, Florida, United States

The final, formatted version of the article will be published soon.

    The development of medical countermeasures (MCMs) against organophosphate (OP) induced poisoning is of substantial importance. Use of conventional therapeutics is complicated by offtarget effects and restricted penetration of the blood-brain barrier (BBB). Therefore, a concerted effort is underway to discover improved acetylcholinesterase (AChE) reactivators, muscarinic acetylcholine receptor (mAChR) antagonists, and other countermeasures with broader spectrum activity and enhanced CNS efficacy. We recently developed a rat brain slice assay to assess the efficacy of AChE reactivators and mAChR antagonists against the acute effects of the organophosphorus AChE inhibitor 4-nitrophenyl isopropyl methylphosphonate (NIMP) in the basolateral amygdala (BLA). Here we introduce a complimentary anesthetized animal model to evaluate the same compounds in vivo with concurrent monitoring of EEG and respiratory rate. We find that intravenous delivery of 0.5 mg/kg NIMP reliably produces seizure like activity in the BLA, with concurrent respiratory depression and eventual respiratory failure. The central effects of AChE reactivators and mAChR antagonists delivered intravenously are consistent with their expected ability to cross the BBB. Combining our previously described in vitro assay with the methods described here provides a relatively comprehensive set of preclinical tools for evaluating the efficacy of novel MCMs. Notably, using these methods potentially obviates subjecting conscious animals to cholinergic crises, which aligns with the AAALAC's 3Rs principle of refinement.

    Keywords: organophosphates, basolateral amygdala, Acetylcholinesterase, AChE, Status Epilepticus, NIMP, HI-6

    Received: 29 Feb 2024; Accepted: 25 Jun 2024.

    Copyright: © 2024 Thinschmidt, Talton, Harden and Frazier. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Charles J. Frazier, University of Florida, Gainesville, 32609, Florida, United States

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