The slides were submerged in electrophoretic buffer (pH >13) to unwind the nuclear DNA for 1hr and then subjected to electrophoresis in the same buffer. The electrophoresis was carried out at 2V/cm and 300 mA; for 30 min. Following electrophoresis the gels were neutralized in 400 mM Tris-HCl pH 7.5 for 15 min. The damaged DNA traveled toward the anode during electrophoresis and formed an image of a “comet” tail. After staining the slides with ethidium bromide (20 μg/mL) the comets were detected and quantified as described below.