Mercury-induced toxicity of rat cortical neurons is mediated through N-methyl-D-Aspartate receptors
1 Department of Cell Biology & Anatomy, University of Calgary, Alberta, Canada
2 Physiology & Pharmacology, Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Alberta, Canada
Molecular Brain 2012, 5:30 doi:10.1186/1756-6606-5-30Published: 14 September 2012
Mercury is a well-known neurotoxin implicated in a wide range of neurological or psychiatric disorders including autism spectrum disorders, Alzheimer’s disease, Parkinson’s disease, epilepsy, depression, mood disorders and tremor. Mercury-induced neuronal degeneration is thought to invoke glutamate-mediated excitotoxicity, however, the underlying mechanisms remain poorly understood. Here, we examine the effects of various mercury concentrations (including pathological levels present in human plasma or cerebrospinal fluid) on cultured, rat cortical neurons.
We found that inorganic mercuric chloride (HgCl2 –at 0.025 to 25 μM) not only caused neuronal degeneration but also perturbed neuronal excitability. Whole-cell patch-clamp recordings of pyramidal neurons revealed that HgCl2 not only enhanced the amplitude and frequency of synaptic, inward currents, but also increased spontaneous synaptic potentials followed by sustained membrane depolarization. HgCl2 also triggered sustained, 2–5 fold rises in intracellular calcium concentration ([Ca2+]i). The observed increases in neuronal activity and [Ca2+]i were substantially reduced by the application of MK 801, a non-competitive antagonist of N-Methyl-D-Aspartate (NMDA) receptors. Importantly, our study further shows that a pre incubation or co-application of MK 801 prevents HgCl2-induced reduction of cell viability and a disruption of β-tubulin.
Collectively, our data show that HgCl2-induced toxic effects on central neurons are triggered by an over-activation of NMDA receptors, leading to cytoskeleton instability.