Effects of bupivacaine and ropivacaine on field potential in rat hippocampal slices

In spite of more than 20 yr of research, the mechanism whereby local anaesthetics act on the brain to mediate anaesthesia still remains unclear. Furthermore, the effect of local anaesthetics on neuronal excitability and synaptic transmission in the hippocampus has not been reported. Thus, the purpose of the present study was to find out the differences between the local anaesthetics, bupivacaine and ropivacaine, in their actions on synaptic transmission of brain in the context of hippocampal field potential. Brains were removed from 3- to 4-week-old rats and transverse slices (300 mu m thick) were prepared using a microslicer. A slice was then placed on the centre on a multielectrode dish probe. To record evoked field potentials at 64 sites, a pair of single planar microelectrodes delivering bipolar constant current pulses (45-90 mu A, 0.1 ms) was applied. Electrophysiological recordings were measured using the 64-channel multielectrode dish. The amplitude of field potential in the rat CA1 region was inhibited by both bupivacaine and ropivacaine. The inhibitory effects of bupivacaine and ropivacaine on field potential amplitudes in CA1 were similar. For bupivacaine 10 mu g ml(-1), inhibited field potentials were incompletely recovered; in contrast, for 10 ropivacaine mu g ml(-1), inhibited field potentials were completely recovered after washing out with incubation solution. Inhibitory effects of bupivacaine and ropivacaine on hippocampal field potential amplitude and recovery rate after washout after bupivacaine or ropivacaine treatment represent the underlying mechanisms of the systemic toxicity of local anaesthetics.