AGONIST EFFECTS AT PUTATIVE CENTRAL 5-HT(4)RECEPTORS IN RAT HIPPOCAMPUS BY R(+)-ZACOPRIDE AND S(-)-ZACOPRIDE - NO EVIDENCE FOR STEREOSELECTIVITY

The EEG of halothane anaesthetized rats was recorded from an electrode implanted into the hippocampus. In the present study the effect of R(+)- and S()-zacopride, administered intra-cerebroventricularly, on different frequency bands of the EEG was investigated. Both enantiomers induced similar dose-dependent (5-20-mu-g) increases in all frequency bands. The effects of R(+)- and S()-zacopride were inhibited by pretreatment with a high dose of ICS 205-930 (1-mu-g i.c.v.), which suggests the involvement of 5-HT4 receptors. The lack of stereo-selectivity of the zacopride enantiomers is in contrast to observations made in in vitro studies.