Please cite this article in press as: Olczak M, et al. Persistent behavioral impairments and alterations of brain dopamine system after early postnatal administration of thimerosal in rats. Behav Brain Res (2011), doi:10.1016/j.bbr.2011.04.026 ARTICLE IN PRESS G Model BBR 7072 1–12 Behavioural Brain Research xxx (2011) xxx–xxx 1 Contents lists available at ScienceDirect Behavioural Brain Research journal homepage: www.elsevier.com/locate/bbr Research report 1 Persistent behavioral impairments and alterations of brain dopamine system after early postnatal administration of thimerosal in rats 2 3 Mieszko Olczak a,d , Michalina Duszczyk a , Pawel Mierzejewski b , Ksenia Meyza c , Maria Dorota Majewska a,e,* 4 5 a Marie Curie Chairs Program at the Department of Pharmacology and Physiology of the Nervous System, Institute of Psychiatry and Neurology, 02-957 Warsaw, Poland 6 b Department of Pharmacology and Physiology of the Nervous System, Institute of Psychiatry and Neurology, 02-957 Warsaw, Poland 7 c Department of Neurophysiology, Nencki Institute of Experimental Biology, PAS, Pasteur 3 Str., 02-093 Warsaw, Poland 8 d Department of Forensic Medicine, Medical University of Warsaw, Oczki 1 Str., 02-007 Warsaw, Poland 9 e Department of Biology and Environmental Science, University of Cardinal Stefan Wyszynski, Wóycickiego Str. 1/3, 01-815 Warsaw, Poland 10 11 article info 12 13 Article history: 14 Received 5 November 2010 15 Received in revised form 14 April 2011 16 Accepted 20 April 2011 17 Available online xxx 18 Keywords: 19 Thimerosal 20 Rat 21 Neurodevelopment 22 Impairment 23 Behavior 24 Dopamine 25 abstract The neurotoxic organomercurial thimerosal (THIM), used for decades as vaccine preservative, is a sus- pected factor in the pathogenesis of some neurodevelopmental disorders. Previously we showed that neonatal administration of THIM at doses equivalent to those used in infant vaccines or higher, causes lasting alterations in the brain opioid system in rats. Here we investigated neonatal treatment with THIM (at doses 12, 240, 1440 and 3000 g Hg/kg) on behaviors, which are characteristically altered in autism, such as locomotor activity, anxiety, social interactions, spatial learning, and on the brain dopaminergic system in Wistar rats of both sexes. Adult male and female rats, which were exposed to the entire range of THIM doses during the early postnatal life, manifested impairments of locomo- tor activity and increased anxiety/neophobia in the open field test. In animals of both sexes treated with the highest THIM dose, the frequency of prosocial interactions was reduced, while the frequency of asocial/antisocial interactions was increased in males, but decreased in females. Neonatal THIM treatment did not significantly affect spatial learning and memory. THIM-exposed rats also manifested reduced haloperidol-induced catalepsy, accompanied by a marked decline in the density of striatal D 2 receptors, measured by immunohistochemical staining, suggesting alterations to the brain dopamin- ergic system. Males were more sensitive than females to some neurodisruptive/neurotoxic actions of THIM. These data document that early postnatal THIM administration causes lasting neurobehav- ioral impairments and neurochemical alterations in the brain, dependent on dose and sex. If similar changes occur in THIM/mercurial-exposed children, they could contribute do neurodevelopmental disorders. © 2011 Published by Elsevier B.V. 1. Introduction 26 Thimerosal (THIM; sodium ethyl-mercurithiosalicylate; con- 27 taining approximately 49% of mercury (Hg) by weigh), has been 28 added to pediatric vaccines as a preservative since the 1930s (and 29 still is in many developing countries), without being adequately 30 tested for safety in developing organisms. In the body THIM is 31 metabolized first to ethyl-mercury and further to inorganic mer- 32 cury compounds, which accumulate in the brain and other vital 33 Abbreviations: THIM, thimerosal; DA, dopamine; ASD, autism spectrum disor- ders. * Corresponding author at: Department of Pharmacology and Physiology of the Nervous System, Institute of Psychiatry and Neurology, Sobieskiego 9 Str., 02-957 Warsaw, Poland. Tel.: +48 22 45 82 778; fax: +48 22 84 27 664. E-mail address: majewska@ipin.edu.pl (M.D. Majewska). organs [1,2]. With increasing numbers of vaccines injected to pro- 34 gressively younger infants (some only a few hours old), a legitimate 35 concern emerged that Hg from vaccines accumulating in infant 36 brains might contribute to the epidemics of neurodevelopment dis- 37 orders in children [3–9]. This issue is a subject of hot debates, but 38 still remains controversial. 39 Concerns related to use of THIM in pediatric vaccines stem 40 primarily from its neurotoxicity, analogous to that of other mer- 41 curials. THIM has been shown to kill neurons by apoptosis and 42 necrosis in vitro at nanomolar and low micromolar concentrations, 43 which might be reached in the brain after vaccination [10–15]. 44 The molecular mechanisms of THIM-induced neurotoxicity involve 45 DNA breakage [10,16], depolarization and damage of mitochondrial 46 membranes [11,15], generation of reactive oxygen species, release 47 of cytochrome and apoptosis inducing factors from mitochondria 48 to cytosol, and activation of caspases 9 and 3, known toparticipate 49 0166-4328/$ – see front matter © 2011 Published by Elsevier B.V. doi:10.1016/j.bbr.2011.04.026