Drugs that increase monoamine neurotransmission are effective in both anxiety and depression. The therapeutic effects of monoamine-based antidepressant drugs may involve indirect effects on neurotransmission through α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors (AMPAR).Thus, chronic antidepressant treatment increases AMPAR-mediated neurotransmission, and AMPAR positive allosteric modulators (APAMs) have shown antidepressant-like efficacy in rodents. Here, the effect of enhanced AMPAR neurotransmission on the antidepressant-like and anxiolytic-like actions of the selective serotonin reuptake inhibitor (SSRI) citalopram (0-10 mg/kg) was investigated in mice, using the APAM LY451646 (0-3 mg/kg). Antidepressant-like effects were assessed with the forced swim test (FST), while anxiolytic-like effects were tested with the elevated zero maze (EZM) and the marble burying test (MBT). LY451646 (3 mg/kg) increased swim distance in the FST and a sub-active dose of LY451646 (1 mg/kg) enhanced the effect of citalopram in the FST. In the EZM, LY451646 (3 mg/kg) did not show anxiogenic effects alone, but blocked the anxiolytic-like action of citalopram in the EZM, as reflected by an increase in the latency to enter the open areas and a decrease in the number of entries and time spent in the open areas in citalopram-treated mice. In the MBT, LY451646 (3 mg/kg) showed no effect alone but significantly attenuated the anxiolytic-like effect of citalopram (1.25-2.5 mg/kg) by increasing the number of marbles buried in citalopram-treated mice. These results suggest that AMPAR neurotransmission plays opposite roles in anxiety and depression, as AMPAR potentiation facilitated the antidepressant-like effects of citalopram while attenuating its anxiolytic-like effect. These findings have ramifications in the search for AMPAR-based novel anxiolytic and antidepressant treatments.