The effects of selective antagonists of serotonin 5-HT7 and 5-HT1A receptors on MK-801-induced impairment of learning and memory in the passive avoidance and Morris water maze tests in rats: mechanistic implications for the beneficial effects of the novel atypical antipsychotic lurasidone.

We have previously reported that lurasidone, a novel atypical antipsychotic with potent serotonin 5-HT(7) antagonist and 5-HT(1A) partial agonist activities, is superior to other antipsychotics in improving the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801-induced learning and memory impairment in the passive avoidance (PA) and Morris water maze (MWM) tests in rats. In this study, we investigated the effects of selective antagonists of 5-HT(7) and 5-HT(1A) receptors (SB-656104-A and WAY-100635, respectively) on MK-801-induced learning and memory impairment in the same tests. In the PA test, either pre-training (3 and 10mg/kg, p.o.) or post-training (0.3mg/kg, i.v.) administration of lurasidone significantly reversed the test response impaired by MK-801, consistent with our previous reports. Pre-training administration of either SB-656104-A (10 and 30 mg/kg, i.p.) or WAY-100635 (1mg/kg, s.c.) also significantly reversed MK-801-induced memory impairment. Furthermore, post-training administration of either SB-656104-A (0.3mg/kg, i.v.) or WAY-100635 (0.01 mg/kg, i.v.) counteracted the effect of MK-801, which suggested that both 5-HT receptor subtype-selective antagonists could restore the memory consolidation process. In the MWM test, SB-656104-A (3mg/kg, i.p.) reversed learning impairment induced by MK-801. On the other hand, WAY-100635 (0.3 and 1mg/kg, i.p.) did not have any effect on the MK-801-induced learning impairment. Taken together, our results showed that 5-HT(7) and 5-HT(1A) receptor antagonists mimic the effect of lurasidone in whole or in part, respectively, to reverse MK-801-induced learning and memory impairment, which warrants further investigation of the interaction of lurasidone with these serotonin receptors as a possible mechanism underlying its procognitive effects in these animal models.