Organophosphate neurotoxicity: chronic effects of sarin on the electroencephalogram of monkey and man
Neurobehav Toxicol Teratol, 4 (6):
767-778 (November 1982)Description
In 1982, scientists injected monkeys with toxic levels of the organophosphate sarin (related to common pesticides) and did EEG scans to measure neurotoxicity. The scientists found that the neurotoxic exposure revealed signs of excitotoxic activity in the monkeys' brains directly after the exposure, but importantly, the changes remained even a year after the exposure, long after traces of sarin could be found in their blood.
In another group of monkeys, they injected 10 small doses, spaced-out a week apart—doses that, on their own, are not deemed toxic—and measured the results. They found that these low doses, taken together, produced the same excitotoxic brain changes as the single toxic dose—these changes, too, were observed a year later.
This suggests that a) the excitotoxic effects of toxics on the brain persist long after the agent has been metabolized by the body, and b) even low doses of toxic exposures, exposures that are not, on their own, enough to cause neurotoxic activity, can cumulatively add up to result in damaging and lasting effects on our health. As many of us know from personal experience, it's not just one high-exposure event that can trigger these long-lasting changes; it can be done by repeated low-level exposures, too.
This study is referenced in the Discover article about TILT. Here is the context from the article:
“The lack of a blood-brain barrier in the olfactory system allows chemicals direct access to the limbic system,” says Miller. “And the olfactory pathways are already known to be particularly susceptible to electrical and chemical kindling. Moreover, most chemical exposures are intermittent, which is the kind of exposure known to potentiate kindling and sensitization.” Intermittent lower-dose exposures can be as toxic as a single higher-dose exposure; Miller cites monkey research showing that either 10 nontoxic weekly doses or one toxic dose of an organophosphate pesticide led to the same increase in brain wave activity as measured by electroencephalogram, or EEG.
Miller hypothesizes that exposure to toxicants permanently decreases the threshold needed to excite the limbic network, setting the stage for a phenomenon much like kindling. “It’s not actual kindling in the strict scientific sense of inducing a seizure,” she notes, but that sensitization could theoretically lead to permanent changes in function — and permanently increased reactivity to chemicals processed through the olfactory neurons.