Visualizing DNA single- and double-strand breaks in the Flash comet assay by DNA polymerase-assisted end-labelling.

In the comet assay, tails are formed after single-cell gel electrophoresis if the cells have been exposed to genotoxic agents. These tails include a mixture of both DNA single-strand breaks (SSBs) and double-strand breaks (DSBs). However, these two types of strand breaks cannot be distinguished using comet assay protocols with conventional DNA stains. Since DSBs are more problematic for the cells, it would be useful if the SSBs and DSBs could be differentially identified in the same comet. In order to be able to distinguish between SSBs and DSBs, we designed a protocol for polymerase-assisted DNA damage analysis (PADDA) to be used in combination with the Flash comet protocol, or on fixed cells. By using DNA polymerase I to label SSBs and terminal deoxynucleotidyl transferase to label DSBs with fluorophore-labelled nucleotides. Herein, TK6-cells or HaCat cells were exposed to either hydrogen peroxide (H2O2), ionising radiation (X-rays) or DNA cutting enzymes, and then subjected to a comet protocol followed by PADDA. PADDA offers a wider detection range, unveiling previously undetected DNA strand breaks.

Exposure to lidocaine in early life does not cause negative long-term behavioural changes in mice.

BACKGROUND: The local anaesthetic lidocaine is widely used in the neonatal intensive unit to treat seizures in premature babies. However, other antiepileptics administered during early development in various animal models have shown negative long-term behavioural effects. Since no long-term behavioural data so far exist regarding lidocaine exposure at an early age, we decided to perform this extended follow-up study using a sensitive behavioural test. METHODS: Neonatal mice received a subcutaneous administration of saline or one dose of lidocaine (0.5, 4, or 12 mg kg-1) on postnatal day 10 (P10; peak of the Brain Growth Spurt). A well-established test to detect long-term behavioural alterations was conducted at 2 and 6 months of age, corresponding to early and late adulthood in humans. RESULTS: All animal survived to later testing. No signs of acute toxicity were observed. Lidocaine exposure did not result in any negative behavioural effects during habituation to a new home environment at any of the two studied time points, compared to saline placebo. CONCLUSIONS: Lidocaine does not by itself produce any negative long-term behavioural effects in mice exposed in early life (P10) despite long-term follow-up. This is reassuring regarding the current practice of treating seizures in premature babies with intravenous lidocaine.