Effects of Methylmercury on the Microvasculature of the Developing Brain M. Bertossi 1,* , F. Girolamo 2 , M. Errede 2 , D. Virgintino 2 , G. Elia 3 , L. Ambrosi 4 , L. Roncali 2 1 Dipartimento di Scienze Biomediche, Facolta ` di Medicina e Chirurgia, Universita ` di Foggia, via L. Pinto, 71100 Foggia, Italy 2 Department of Human Anatomy and Histology, Bari University, Medical School, Italy 3 S. Maugeri Foundation, IRCSS, Bari, Italy 4 Department of Medical and Occupational Sciences, Foggia University, Italy Received 12 May 2003; accepted 22 December 2003 Available online 5 March 2004 Abstract The study, undertaken with the aim of further investigating the effects of methylmercury (MeHg) exposure on the developing brain, was performed in the cerebellum of chick embryos, chronically treated with a MeHgCl solution dropped onto the chorioallantoic membrane, and in control embryo cerebella. Quantitative evaluations, performed by cold vapour atomic absorption spectrophotometry, demonstrated a high mercury content in the chorioallantoic membrane, ence- phalon, liver and kidney of the treated embryos. The morphological observations showed severe neuronal damage consisting of degenerative changes of thegranules and Purkinje neurons. The effects on astrocytes were even more severe, since they were extremely rare both in the neuropil and around the vessel wall. Compared with the controls, the cerebellar vessels of MeHg-treated embryos showed immature morphology, poor differentiation of endothelial barrier devices, and high permeability to the exogenous protein horseradish peroxidase. These findings support the hypothesis that MeHg- related neuronal sufferance may be secondary to astrocytic damage and suggest that the developmental neurotoxicity of this compound could also be related to astrocyte loss-dependent impairment of blood–brain barrier (BBB) differentiation. # 2004 Elsevier Inc. All rights reserved. Keywords: Methylmercury; Development; Neurotoxicity; Cerebellum; Astrocytes; Blood–brain barrier INTRODUCTION The evidence of the neurotoxicity of methylmercury (MeHg) dates back to the 50s–60s, when it was ascer- tained that the neurological diseases affecting thou- sands of people in Minamata and Niigata (Japan) were caused by consumption of fish contaminated by MeHg (Harada, 1978; Irukayama et al., 1962; Takeuchi et al., 1962). MeHg exposure remains a major public health concern because of natural and anthropogenic release of inorganic mercury into the aquatic environment (Crinnion, 2000; Pirrone, 2001), where it is biotrans- formed by algae and bacteria into MeHg. This can pass along the food chain and, eventually, to man (Jensen and Jernelov, 1969; Wood et al., 1968). Neuropathological changes, such as damage to spe- cific cerebral and cerebellar areas and sensory fibres of the spinal nerves, have been described in both man and laboratory animals exposed to MeHg (Eto, 1997; Gar- man et al., 1975; Hunter and Russell, 1954; Naga- shima, 1997). However, the severity of the damage differs according to exposure time and dose, as well as animal species and age (Berlin, 1986; Burbacher et al., 1990; Kakita et al., 2000a,b; Wakabayashi et al., 1995; WHO, 1993; Willes, 1977). The developing brain is extremely sensitive to MeHg poisoning; it is well known, in fact, that prolonged pre- and/or perinatal exposure to MeHg, even at moderate doses, results in widespread neuronal damage, severe NeuroToxicology 25 (2004) 849–857 * Corresponding author. Tel.: þ39-0805478310; fax: þ39-0805478310. E-mail addresses: bertossi@histology.uniba.it, m.bertossi@unifg.it (M. Bertossi). 0161-813X/$ – see front matter # 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.neuro.2004.01.005