Serotonin produces a reversible concentration dependent decrease of population spikes in rat hippocampal slices

Superfusion of slices of rat dorsal hippocampus in vitro with serotonin (5-HT) reversibly decreases the amplitude of the CA1 population spike evoked by stimulation of stratum radiatum. The magnitude of the drug effect is concentration dependent and is greater on submaximal than on maximal population spikes. Concentration-response curves were generated using population spikes 30-60% of maximum by superfusion with increasing concentrations of 5-HT interspersed with perfusion of drug free medium. The EC50 for 5-HT was 3.2 microM. Repeated applications of a maximal dose of 5-HT did not produce tachyphylaxis. The reversibility, reproducibility and concentration dependence of the 5-HT response in the rat hippocampal slice makes this preparation useful for rigorous pharmacological classification of the receptor(s) involved.