Effects of physostigmine and scopolamine on long-term potentiation of hippocampal population spikes in rats

To elucidate an involvement of the cholinergic system in the long-term potentiation phenomenon, effects of physostigmine and scopolamine on population spike and its long-term potentiation in the dentate granule cell layer of anesthetized rats and in the CA1 pyramidal cell layer of rat hippocampal slices were examined. In anesthetized rats, physostigmine (0.01 mg/kg, i.v.) enhanced at a late phase the long-term potentiation induced by tetanic stimulation (15 Hz, 15 s, 7.5 times the threshold for population spike) of the perforant path, while scopolamine (1.0 mg/kg) suppressed it at an early phase. The two drugs did not affect the population spike itself. The time course of the long-term potentiation under the treatment of physostigmine was similar to that induced by stronger tetanic stimulation (10 times the threshold). In hippocampal slices, physostigmine (10(-6)M) showed a tendency to enhance the long-term potentiation induced by tetanic stimulation (15 Hz, 15 s, 5 times the threshold) of the stratum radiatum, with an increase of the population spike itself. Scopolamine (10(-5)M) markedly suppressed the long-term potentiation with a decrease of the population spike itself. From these results, it is suggested that cholinergic modification by physostigmine or scopolamine affects the long-term potentiation phenomenon in the hippocampus under the in vivo and in vitro conditions.