5-Hydroxytryptamine4-Like Receptors Mediate the Slow Excitatory Response to Serotonin in the Rat Hippocampus1

Hippocampal pyramidal neurons of the CAl region express 5-hydroxytryptamine (serotonin, 5-HI) receptors which, upon ac-tivation, elicit a slow membrane depolarization and a decrease in the calcium-activated afterhyperpolanzation present in these cells. Previous electrophysiological studies have shown that this receptor(s) exhibits a pharmacological profile similar to that of the 5-HT1, 5-HI3 and 5-HT4 subtypes. In the present study, intracellular recordings in rat brain slices were used in order to examine the effects of a variety of compounds that distinguish between these receptor subtypes. Administration of 5-HT in the presence of a 5-HTIA receptor antagonist elicited a depolarization and a concentration-dependent reduction in the amplitude of the afterhyperpolanzation. These effects were mimicked by 5-meth-oxytryptamine and 5-carboxyamidotryptamine but not by 2-methyl-S-HI or phenylbiguanide. Administration of the benzam