Pyridostigmine brain penetration under stress enhances neuronal excitability and induces early immediate transcriptional response

Abstract

Pyridostigmine, a carbamate acetylcholinesterase (AChE) inhibitor, is routinely employed in the treatment of the autoimmune disease myasthenia gravis. Pyridostigmine is also recommended by most Western armies for use as pretreatment under threat of chemical warfare, because of its protective effect against organophosphate poisoning. Because of this drug's quaternary ammonium group, which prevents its penetration through the blood-brain barrier, the symptoms associated with its routine use primarily reflect perturbations in peripheral nervous system functions. Unexpectedly, under a similar regimen, pyridostigmine administration during the Persian Gulf War resulted in a greater than threefold increase in the frequency of reported central nervous system symptoms. This increase was not due to enhanced absorption (or decreased elimination) of the drug, because the inhibition efficacy of serum butyryl-cholinesterase was not modified. Because previous animal studies have shown stress-induced disruption of the blood-brain barrier, an alternative possibility was that the stress situation associated with war allowed pyridostigmine penetration into the brain. Here we report that after mice were subjected to a forced swim protocol (shown previously to simulate stress), an increase in blood-brain barrier permeability reduced the pyridostigmine dose required to inhibit mouse brain AChE activity by 50% to less than 1/100th of the usual dose. Under these conditions, peripherally administered pyridostigmine increased the brain levels of c-fos oncogene and AChE mRNAs. Moreover, in vitro exposure to pyridostigmine increased both electrical excitability and c-fos mRNA levels in brain slices, demonstrating that the observed changes could be directly induced by pyridostigmine. These findings suggest that peripherally acting drugs administered under stress may reach the brain and affect centrally controlled functions.

A re-examination of neuropsychological functioning in Persian Gulf War era Veterans

“…In addition, these veterans also showed lower salivary cortisol levels than their non-PTSD counterparts suggesting dysregulated immune system functioning (Kellner et al, 1999). However, we were unable to confirm any health complications from the synergistic effects of small doses of neurotoxicants combined with a stress induced reduction in immune functioning (Friedman et al, 1996) in our original evaluation of 200 GW veterans. In sum, there are several competing hypotheses for the varied symptoms reported by PGW veterans.…”

“…Other researchers suggest that prolonged stress can lead to long-term hormonal changes (Yehuda, 1997), reduced immune system functioning, (Black, 1994) and alterations of brain neurotransmitters that mediate cognitive and psychological responses (Wolfe & Charney, 1991). Reports of animal models suggest that acute stress may also alter the permeability of the blood brain barrier to particular neurotoxicants (including pyridostigmine bromide; an acetylcholinesterase inhibitor given prophylactically to PGW veterans as a protective measure in the event of chemical weapon attack (Friedman et al 1996). However, other reports of different rodent species could not replicate these findings (Lallement, 1998 ).…”

Protein binding of isofluorophate in vivo after coexposure to multiple chemicals.

“…The brain data show some significant differences consistent among all pesticide exposures. PYB does not easily pass the rodent blood-brain barrier, even under stressed conditions (31,32), although one study suggests otherwise (33). The compounds, even in total, remain at tracer concentrations (~100 nM maximum whole-body average for PYB) that can cause only minor competitive inhibition of proteins.…”

Beyond the usual suspects: a cholinergic route for panic attacks

“…Kaufer and colleagues 25 showed that acute stress of even moderate intensity (eg, a single session of 4 min forced swimming in mice)-as well as inhibitors of acetylcholinesterase (AChE)-produce a transient increase in the amount of released ACh in corticohippocampal areas, independent of the pituitary-adrenocortical axis. 26 Consequences include an early phase of enhanced neuronal excitability, 27 and most interest-ingly, long-lasting (up to 3 h in vitro) modulation of the genetic regulation of ACh availability 25 in the CNS. More specifically (see Figure 1), following acute stress and ACh release, the central muscarinic receptors mediate the induction of the gene encoding the early immediate transcription factor c-Fos.…”

“…More specifically (see Figure 1), following acute stress and ACh release, the central muscarinic receptors mediate the induction of the gene encoding the early immediate transcription factor c-Fos. 27 This produces, by a Ca 2+ -dependent mechanism, enhanced c-Fos binding to a site close to the promoter regions of genes with key roles for acetylcholine function, namely the gene encoding acetylcholinesterase (AchE), the gene for the acetylcholine-synthetizing enzyme choline acetyltransferase (ChAT), and the vescicular acetylcholine transporter (VAChT). RNA analyses clearly show 25 that more AChE is then produced, while synthesis of both ChAT and VAChT decreases.…”