Opposing effects of AMPA and 5-HT1A receptor blockade on passive avoidance and object recognition performance: Correlation with AMPA receptor subunit expression in rat hippocampus

It has been suggested that antagonists at serotonin 5-HT1A receptors may exert a procognitive effect by facilitating glutamatergic neurotransmission. Here we further explored this issue by looking for the ability of a 5-HT1A antagonist to prevent the learning deficit induced by AMPA receptor blockade in two behavioural procedures in rats, and for concomitant molecular changes presumably involved in memory formation in the hippocampus. Pretraining administration of the competitive AMPA receptor antagonist, NBQX, produced a dose-related retention impairment in a passive avoidance task 24 h later, and also impaired retention in a novel object recognition test when an intertrial interval of 3 h was selected. Pretreatment with the selective 5-HT1A receptor antagonist, WAY-100635, prevented the learning deficit induced by NBQX in the two behavioural procedures. In biochemical studies performed on rat hippocampus after the retention tests, we found that learning increased the membrane levels of AMPA receptor GluR1 and GluR2/3 subunits, as well as the phosphorylated forms of GluR1, effects that were abolished by NBQX administration before the training session. Pretreatment with WAY-100635 counteracted the NBQX effects and restored the initial learning-specific increase in Ca2+/calmodulin-dependent protein kinase II (CaMKII) function and the later increase in GluR2/3 and phosphorylated GluR1 surface expression. Moreover, administration of WAY-100635 before object recognition training improved recognition memory 24 h later and potentiated the learning-associated increase in AMPA receptor subunits. The results support the proposed utility of 5-HT1A antagonists in the treatment of cognitive disorders.