Neurochem Res. 2010 Aug 28.
Neonatal Administration of Thimerosal Causes Persistent Changes in Mu Opioid Receptors in the Rat Brain.
Department of Pharmacology and Physiology  of the Nervous System, Institute of Psychiatry and Neurology, Sobieskiego 9 str., 02-957, Warsaw, Poland.
Abstract
Thimerosal  added to some pediatric vaccines is suspected in pathogenesis of  several neurodevelopmental disorders. Our previous study showed that  thimerosal administered to suckling rats causes persistent, endogenous  opioid-mediated hypoalgesia. Here we examined, using immunohistochemical  staining technique, the density of mu-opioid receptors (MORs) in the  brains of rats, which in the second postnatal week received four i.m.  injections of thimerosal at doses 12,  240, 1,440 or 3,000 mug Hg/kg. The periaqueductal gray, caudate putamen  and hippocampus were examined. Thimerosal administration caused  dose-dependent statistically significant increase in MOR densities in  the periaqueductal gray and caudate putamen, but decrease in the dentate  gyrus, where it was accompanied by the presence of degenerating neurons  and loss of synaptic vesicle marker (synaptophysin). These data  document that exposure to thimerosal during early postnatal life  produces lasting alterations in the densities of brain opioid receptors  along with other neuropathological changes, which may disturb brain  development.
 
