title: Effects of methylmercury on spinal cord afferents and efferents-A review.
abstract: Methylmercury (MeHg) is an environmental neurotoxicant of public health concern. It readily accumulates in exposed humans, primarily in neuronal tissue. Exposure to MeHg, either acutely or chronically, causes severe neuronal dysfunction in the central nervous system and spinal neurons; dysfunction of susceptible neuronal populations results in neurodegeneration, at least in part through Ca2+-mediated pathways. Biochemical and morphologic changes in peripheral neurons precede those in central brain regions, despite the fact that MeHg readily crosses the blood-brain barrier. Consequently, it is suggested that unique characteristics of spinal cord afferents and efferents could heighten their susceptibility to MeHg toxicity. Transient receptor potential (TRP) ion channels are a class of Ca2+-permeable cation channels that are highly expressed in spinal afferents, among other sensory and visceral organs. These channels can be activated in numerous ways, including directly via chemical irritants or indirectly via Ca2+release from intracellular storage organelles. Early studies demonstrated that MeHg interacts with heterologous TRP channels, though definitive mechanisms of MeHg toxicity on sensory neurons may involve more complex interaction with, and among, differentially-expressed TRP populations. In spinal efferents, glutamate receptors of the N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and possibly kainic acid (KA) classes are thought to play a major role in MeHg-induced neurotoxicity. Specifically, the Ca2+-permeable AMPA receptors, which are abundant in motor neurons, have been identified as being involved in MeHg-induced neurotoxicity. In this review, we will describe the mechanisms that could contribute to MeHg-induced spinal cord afferent and efferent neuronal degeneration, including the possible mediators, such as uniquely expressed Ca2+-permeable ion channels.
authors.affiliation: Department of Pharmacology and Toxicology, 1355 Bogue Street, Life Sciences Building Rm. B440, Michigan State University, East Lansing, MI, United States; Institute for Integrative Toxicology, 1129 Farm Lane, Food Safety and Toxicology Rm. 165, Michigan State University, East Lansing, MI, United States; Comparative Medicine and Integrative Biology Program, 784 Wilson Road, Veterinary Medical Center Rm. G-100, Michigan State University, East Lansing, MI, United States. Electronic address: colonro1@msu.edu.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Colón-Rodríguez
authors.affiliation: Department of Pharmacology and Toxicology, 1355 Bogue Street, Life Sciences Building Rm. B440, Michigan State University, East Lansing, MI, United States; Institute for Integrative Toxicology, 1129 Farm Lane, Food Safety and Toxicology Rm. 165, Michigan State University, East Lansing, MI, United States; Comparative Medicine and Integrative Biology Program, 784 Wilson Road, Veterinary Medical Center Rm. G-100, Michigan State University, East Lansing, MI, United States. Electronic address: hehannon@iupui.edu.
authors.forename: Heidi E
authors.initials: HE
authors.lastname: Hannon
authors.affiliation: Department of Pharmacology and Toxicology, 1355 Bogue Street, Life Sciences Building Rm. B440, Michigan State University, East Lansing, MI, United States; Institute for Integrative Toxicology, 1129 Farm Lane, Food Safety and Toxicology Rm. 165, Michigan State University, East Lansing, MI, United States; Comparative Medicine and Integrative Biology Program, 784 Wilson Road, Veterinary Medical Center Rm. G-100, Michigan State University, East Lansing, MI, United States. Electronic address: atchiso1@msu.edu.
authors.forename: William D
authors.initials: WD
authors.lastname: Atchison
mesh_terms: D000818:Animals; D004525:Efferent Pathways / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008767:Methylmercury Compounds / Q000633:toxicity*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000187:drug effects* / Q000378:metabolism; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism; D017833:Visceral Afferents / Q000187:drug effects / Q000378:metabolism
chemical_list: D008767:Methylmercury Compounds