Behavioral, cellular and molecular maladaptations covary with exposure to pyridostigmine bromide in a rat model of gulf war illness pain

• Published in: Toxicology and applied pharmacology Vol. 352; pp. 119 - 131
• Main Authors: Cooper, B.Y., Flunker, L.D., Johnson, R.D., Nutter, T.J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.2018
• Subjects: Chronic Pain; Gulf War Illness; Muscarinic; Nav1.9; Pyridostigmine; TRPA1; Gulf War Illness; Pyridostigmine; Muscarinic; TRPA1; Nav1.9; Chronic Pain; Na(v)1.9
• ISSN: 0041-008X; 1096-0333
• DOI: 10.1016/j.taap.2018.05.023

Many veterans of Operation Desert Storm (ODS) struggle with the chronic pain of Gulf War Illness (GWI). Exposure to insecticides and pyridostigmine bromide (PB) have been implicated in the etiology of this multisymptom disease. We examined the influence of 3 (DEET (N,N-diethyl-meta-toluamide), permethrin, chlorpyrifos) or 4 GW agents (DEET, permethrin, chlorpyrifos, pyridostigmine bromide (PB)) on the post-exposure ambulatory and resting behaviors of rats. In three independent studies, rats that were exposed to all 4 agents consistently developed both immediate and delayed ambulatory deficits that persisted at least 16 weeks after exposures had ceased. Rats exposed to a 3 agent protocol (PB excluded) did not develop any ambulatory deficits. Cellular and molecular studies on nociceptors harvested from 16WP (weeks post-exposure) rats indicated that vascular nociceptor Nav1.9 mediated currents were chronically potentiated following the 4 agent protocol but not following the 3 agent protocol. Muscarinic linkages to muscle nociceptor TRPA1 were also potentiated in the 4 agent but not the 3 agent, PB excluded, protocol. Although Kv7 activity changes diverged from the behavioral data, a Kv7 opener, retigabine, transiently reversed ambulation deficits. We concluded that PB played a critical role in the development of pain-like signs in a GWI rat model and that shifts in Nav1.9 and TRPA1 activity were critical to the expression of these pain behaviors. •Pain-like behaviors were dependent upon exposure to pyridostigmine bromide (PB).•Voltage dependence of nociceptor Nav1.9 varied with the presence and absence of PB.•Excitability was increased in nociceptors following exposure to Gulf War chemicals.•Exaggeration of muscarinic activation of nociceptor TRPA1 was PB dependent.•The Kv7 opener, retigabine, temporarily reversed established pain-like behaviors.