The synergistic effect of fluoxetine on the locomotor hyperactivity induced by MK-801, a non-competitive NMDA receptor antagonist.

It was found previously that the MK-801 (an uncompetitive NMDA receptor antagonist)-induced locomotor hyperactivity in rats was potently increased by antidepressant drugs. The present paper analysed the locomotor hyperactivity induced by combined treatment with fluoxetine + MK-801 in male Wistar rats. The MK-801 hyperactivity was increased by citalopram (the latter effect was prevented by zacopride and ketanserin), sertraline, p-chloramphetamine, 8-OH-DPAT and TFMPP. The hyperlocomotion caused by fluoxetine + MK-801 was antagonized by tropisetron and zacopride and, to a lesser extent, by ketanserin, ritanserin and NAN-190, but not by WAY 100135, pindolol, metergoline or mianserin. Sulpiride and clozapine were able to inhibit the fluoxetine + MK-801 hyperlocomotion. The hyperlocomotion induced by D-amphetamine or apomorphine was not modified by fluoxetine or citalopram. Fluoxetine increased the release of dopamine (measured by a microdialysis method) in the striatum, induced by MK-801. The obtained results indicate that fluoxetine increases the MK-801-induced locomotor hyperactivity via activation of 5-HT3 receptors and, to a lesser degree, 5-HT2 ones.