Patch-clamp recording techniques were used to examine the effect of serotonin (5HT) upon interneurones contained in the stratum oriens layer of hippocampal slices. Bath application of 1-20 mu M 5HT depolarized neurones by the induction of an inward current at -60 mV. This inward current was Na+-dependent in nature, was mimicked by the 5HT(2) receptor agonist 1 -(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and was inhibited by pre-incubation with the 5HT2 receptor antagonist ritanserin. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.