EFFECTS OF REPEATED TREATMENT WITH FLUOXETINE AND CITALOPRAM, 5-HT UPTAKE INHIBITORS, ON 5-HT1A AND 5-HT2 RECEPTORS IN THE RAT-BRAIN

Repeated treatment with fluoxetine and citalopram, which are potent 5- HT reuptake inhibitors, resulted in different regulation of 5-HT1A and 5-HT2 receptors in the rat brain. Their effects were compared with th ose of other antidepressants: imipramine, mianserin and levoprotiline. The density of 5HT(1A) receptors, labelled with [H-3]8-OH-DPAT, in th e rat hippocampus was enhanced after citalopram, imipramine, mianserin and levoprotiline, but not altered after fluoxetine administration. [ H-3]Ketanserin binding sites, which label 5-HT2 receptors, were increa sed after fluoxetine and levoprotiline, but decreased after citalopram , imipramine and mianserin in the rat cerebral cortex. Acute administr ation of fluoxetine, but not citalopram, resulted in a decreased densi ty of 5HT(1A) receptors. 5-HT2 receptors were not changed by acute adm inistration of either fluoxetine or citalopram. The obtained results i ndicate that besides 5-HT reuptake inhibiting properties of both compo unds, there may exist an additional mechanism(s) of their action, whic h leads to different regulation of 5HT(1A) and 5-HT2 receptors.