Although long-term potentiation was generally initiated by a brief tetanus, in the hippocampus, it could also be evoked by application of the K+ channel blocker tetraethylammonium. The present study was aimed at investigating the effect of lamotrigine, a new anticonvulsant, on the tetraethylammonium-induced potentiation in brain slices of the rat amygdala using intracellular recording techniques. Bath application of tetraethylammonium (20 mM) for 10 min resulted in a long-lasting enhancement of the amplitude of excitatory postsynaptic potentials to 235 ± 12% of control (n=6, P<0.001). Pretreatment of the slices with nifedipine (10 μM) abolished the potentiation, suggesting that tetraethylammonium long-term potentiation in the amygdala is due to Ca2+ influx through voltage- dependent Ca2+ channels. By contrast, N-methyl-D-aspartate receptor activation was not required because D-2-amino-5-phosphonovalerate (50 μM) did not prevent the tetraethylammonium long-term potentiation. Superfusion of lamotrigine (50 μM) depressed the excitatory postsynaptic potential to 53.8 ± 3.9% of control. Tetraethylammonium was subsequently added in the presence of lamotrigine but failed to enhance the excitatory postsynaptic potential. Bursts of Ca2+ spikes evoked by a depolarizing pulse or by synaptic stimulation under tetraethylammonium were depressed by lamotrigine. It is concluded that lamotrigine is capable of inhibiting tetraethylammonium- induced synaptic plasticity. The underlying mechanism is likely due to lamotrigine's inhibition of postsynaptic voltage-dependent Ca2+ channels. Considering that tetraethylammonium is a convulsant agent and brief seizure episodes induced long-term potentiation, fibre sprouting and the development of aberrant synaptic contacts, lamotrigine could be a potential neuroprotective agent, especially in pathological situations where excessive glutamate release occurs.
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