The effects of L-deprenyl (selegiline), a highly selective monoamine oxidase type B (MAO-B) inhibitor, on cell excitability of rat hippocampal CA1 neurons were examined in slice preparations using intracellular recording techniques. Superfusion of L-deprenyl (10 and 20 microM) reversibly limited the repetitive firing (RF) of action potentials elicited by injection of depolarizing current pulses (100 ms) into the pyramidal cells. At a concentration of 1-50 microM, L-deprenyl did not alter resting membrane potential or input resistance of the hippocampal CA1 neurons. The limitation of RF by L-deprenyl (20 microM) was accompanied by the reduction of the maximal rate of rise (Vmax) of the action potentials in a non-voltage-dependent manner. In 80% of recorded cells, application of L-deprenyl (20 microM) produced an increase in the amplitude and duration of afterhyperpolarization (AHP). The limitation of L-deprenyl on RF was mimicked by other MAO-B inhibitors, pargyline and 4-phenylpyridine. In addition, the ability of L-deprenyl to limit RF was not observed in the hippocampal CA1 neurons taken from dopamine (DA)-depleted rats. Moreover, we also observed that the L-deprenyl-induced limitation of RF was specifically antagonized by (+/-)-7-bromo-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzaz epine (SKF-83566, 5 microM), a selective D1 dopaminergic receptor antagonist. However, the D2 dopaminergic receptor antagonist, sulpiride (5 microM), had no effect on L-deprenyl's action. These results indicate that the MAO-B inhibitory ability leading to an increase of the dopaminergic tone in the hippocampus is involved, at least in part, in the L-deprenyl-induced reduction of neuronal excitability in the CA1 region of rat hippocampus and that the D1 dopaminergic receptor is involved in L-deprenyl's action.
Action Potentials Analysis of Variance