exposure perturbs neurite outgrowth and compromises neuronal viability in cultured cortical neurons. Rat cortical neurons were grown either in the absence (A, control) or presence of HgCl2 at 25 nM (B), 100 nM (C), and 25 μM (D) for 3 days. Phase contrast images were taken on day 3. A. Cortical culture under control conditions exhibited healthy population of neurons and glial cells (indicated by a circle), exhibiting extensive neurite outgrowth and network formulation (indicated by an arrow). B. Cells cultured in the presence of 25 nM HgCl2 also developed extensive neurite processes and formed extensive network. C. Neuronal populations cultured in the presence of 100 nM of HgCl2 underwent apoptotic cell death (indicated by an asterisk) and exhibited collapse or retraction of neurites (indicated by an arrow head). D. HgCl2 at 25 μM induced cell death (indicated by asterisks) and inhibited neurite extension and network formation (indicated by an arrow). E &F shows representative confocal images of live/dead assay of cortical neurons cultured either in the absence (E) or presence (F) of 25 μM of HgCl2 for 3 days. Live cell bodies and their neurites were stained with calcein-AM (green), whereas dead cells with compromised membranes were stained with ethidium homodimer-1 (red). Scale bars, 20 μm.