Science Library Category:

Locomotor Activity

Persistent behavioral impairments and alterations of brain dopamine system after early postnatal administration of thimerosal in rats.
Published: 2011

Exposure to thimerosal at vaccine relevant doses alters behavior and brain neurochemistry in a rat model. Based on their findings the authors call for removal of thimerosal from all medicinal products intended for use by children and pregnant women.


Olczak M, Duszczyk M, Mierzejewski P, Meyza K, Majewska MD. Behav Brain Res. 2011 Sep 30;223(1):107-18. doi: 10.1016/j.bbr.2011.04.026. Epub 2011 Apr 28.


The preservative thimerosal added to some vaccines contains about 49% mercury by weight. The toxic effects of thimerosal are dependent on a number of variables including: age of exposure, sex, genetics, tissue concentrations, nutritional adequacy and co-exposures to other toxic chemicals and/or infections. Using a rat animal model, these researchers investigated a series of tests to determine the association of early postnatal exposure to thimerosal on behavioral, neurochemical and neuropathological outcomes. A variety of dose exposures were chosen and were administered by injection i.m. into the glutei maximi in four equal doses on postnatal days 7, 9, 11 and 15. The lowest dose of 12 micro grams of mercury per kilogram of weight was within the range of dose achieved in pediatric vaccines. The higher doses of 240, 1440 and 3000 were used, in part, to account for the lower sensitivity that rats have to the toxic effects of mercury compared to humans. A control cohort received injections of saline. According to the authors, the specific tests utilized were based on behaviors, “which are characteristically altered in autism, such as locomotor activity, anxiety, social interactions, spatial learning, and on the brain dopaminergic system”. Male rats treated with the lowest thimerosal dose (or higher) had a significant reduction in general locomotor activity while in the females this only occurred at the highest thimerosal dose. Such a sexual dimorphism is consistent with males being more sensitive to the neurotoxic property of mercury.

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