Toxicology Letters 201 (2011) 196–204 Contents lists available at ScienceDirect Toxicology Letters journal homepage: www.elsevier.com/locate/toxlet Neurotoxicological effects of low-dose methylmercury and mercuric chloride in developing offspring mice Chun-Fa Huang a,b , Shing-Hwa Liu b , Chuan-Jen Hsu d , Shoei-Yn Lin-Shiau c,∗ a School of Chinese Medicine, College of Chinese Medicine, China Medical University, Taichung, Taiwan b Institute of Toxicology, College of Medicine, National Taiwan University, Taipei, Taiwan c Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan d Department of Otolaryngology, College of Medicine, National Taiwan University, Taipei, Taiwan article info Article history: Received 19 September 2010 Received in revised form 16 December 2010 Accepted 20 December 2010 Available online 30 December 2010 Keywords: Mercurial compounds Perinatal exposure Neurotoxicity Lipid peroxidation Na + /K + -ATPase activities Hg accumulation abstract Mercury is a well-known toxic metal and potently induces severe neurotoxicological effects, especially in infants and children. The purpose of this study was to explore the underlying mechanisms of neurotoxic effects of mercurial compounds on the different stages of developing mice. Low-doses (the probability of human exposure in mercury-contaminated areas) of methylmercury (MeHg) (M, 0.02 mg/kg/day) and mercury chloride (HgCl 2 ) (H, 0.5 mg/kg/day) were administered to mice of the following groups: (1) treatment with distilled water for 7 consecutive weeks after weaning (control-vehicle (CV)); exposure to mercurial compounds at different stages; (2) for 7 consecutive weeks after weaning (control-MeHg (CM) and control-HgCl 2 (CH)); (3) only during perinatal and weaning stages (MeHg-vehicle (MV) and HgCl- vehicle (HV)); and (4) in all experimental stages (MeHg–MeHg (MM) and HgCl 2 –HgCl 2 (HH)). Results revealed the neurobehavioral defects (increased locomotor activities, motor equilibrium impairment, and auditory dysfunction) that correlated with increasing Hg accumulation in CM and CH groups. However, it revealed a decrease and an increase in locomotor activities in MV and HV groups, respectively; these became more severe in MM and HH groups than in MV and HV groups. Motor equilibrium performance in MV and HV groups remained normal, while that in MM and HH groups was decreased. The most severe auditory defects (altered auditory brainstem response, ABR test) found in MM and HH groups than those in the respective CM and CH, MV and HV, including absolute wave III delays and interwave I–III latencies, which suggested that the irreversible auditory dysfunction caused by mercurial compounds. Furthermore, the alteration of lipid peroxidation (LPO), Na + /K + -ATPase activities, and nitric oxide (NO x ) in the brain tissues contributed to the observed neurobehavioral dysfunction and hearing impairment. These findings provide evidence that fetuses were much more susceptible to the effects of mercurial compounds with regard to inducing severely neurotoxicological injuries as that found in human beings. The signaling of ROS/Na + -K + -ATPase/NO x plays a crucial role in the underlying mechanism for mercurial compound-induced toxic effects in offspring. © 2011 Published by Elsevier Ireland Ltd. 1. Introduction Mercury is a toxic heavy metal and a widespread environmen- tal pollutant; its different chemical forms produce varying degrees Abbreviations: MeHg, methylmercury; HgCl2, mercury chloride; CV, control- vehicle; CM, control-MeHg; CH, control-HgCl2; MV, MeHg-vehicle; HV, HgCl2- vehicle; MM, MeHg–MeHg; HH, HgCl2–HgCl2; ABR, auditory brainstem response; LPO, lipid peroxidation; NOx, nitric oxide; BBB, blood–brain barrier; ROS, reactive oxygen species; MDA, malondialdehyde; ICP-MS, inductively coupled plasma mass spectrometry. ∗ Corresponding author at: Institute of Pharmacology, College of Medicine, National Taiwan University, No. 1, Section 1, Jen-Ai Road, Taipei 100, Taiwan. Tel.: +886 2 23123456x88313; fax: +886 2 2391 5297. E-mail address: syshiau@ntu.edu.tw (S.-Y. Lin-Shiau). of toxic effects (Clarkson and Magos, 2006; U.S. Environmental Protection Agency (EPA), 2001). Organic methylmercury (MeHg) is more toxic and penetrates the blood–brain barrier (BBB) more easily than mercuric chloride (HgCl 2 )(Baldi, 1997). Naturally occur- ring inorganic mercurial compounds or effluents from industrial pollution can be converted to MeHg by microorganisms, and the major route of human exposure to mercurial compounds is through dietary intake of mercury-contaminated fish, seafood, grain, or pro- cessed food (Clarkson et al., 2003; Cheng et al., 2006; Shaffi, 1981). During the prenatal or neonatal period, the brain is at high risk and extremely sensitive to toxicants such as MeHg (Burbacher et al., 1990; WHO, 1990). Epidemiological studies in Japan and Iraq have reported that following accidental occupational exposures, or ingestion of contaminated fish or MeHg fungicide-treated grain, infant or child victims suffer acute neurotoxic effects and develop 0378-4274/$ – see front matter © 2011 Published by Elsevier Ireland Ltd. doi:10.1016/j.toxlet.2010.12.016