Effects of arsenite on long-term potentiation in hippocampal slices from young and adult rats

The effects of trivalent arsenite were tested at the Schaffer collateral-CA1 synapse of adult (2–4 month) and young (14–21 days) rats. Exposure of 100 μmol/l arsenite led to a slight and reversible reduction of the amplitudes of evoked excitatory postsynaptic field potentials in adult and young rats, while exposure of 0.1 and 1 μmol/l arsenite had no effects.The long-term potentiation (LTP) was significantly inhibited by arsenite in adult but not in young rats. Exposure of 0.1, 1 and 100 μmol/l arsenite to slices of adult rats before and during the LTP stimulus led to a significant reduction in the potentiated amplitudes amounting to a maximum of 50% of the control values. In young animals, however, exposure of 1 μmol/l arsenite showed no effect on the LTP potentiated amplitudes, while exposure of 100 μmol/l arsenite led initially to a significant reduction in the amplitudes, compared to the control level, which was completely reversible 20 min after washout. Exposure of 100 μmol/l arsenite did not affect the paired-pulse facilitation, indicating that arsenite does not exert its effects by influencing presynaptic transmitter release mechanisms.