Antidepressant- and anxiogenic-like effects of acute 5-HT2C receptor activation in rats exposed to the forced swim test and elevated plus maze

This study investigated the behavioral effects in the forced swim test (FST) and the elevated plus-maze (EPM) of acute administration of WAY 161503 ([4aR]-8,9-dichloro-2,3,4,4a-tetrahydro-1H-pyrazino[1,2-a]quinoxalin-5[6 H]-one), a selective 5-HT2C receptor agonist with putative antidepressant-like properties. Fifteen minutes after intraperitoneal (i.p.) injections of either WAY 161503 (1, 3 and 10 mg/kg) or saline, naive male Wistar rats were exposed to the EPM for 5 min to assess classical and ethological anxiety-like measures. Immediately after EPM exposure, each animal was exposed to the FST, and the latency to the first episode of immobility was recorded (trial session). Twenty-four hours later, the rats were reexposed to a second EPM-FST exposure sequence (test session for FST) under the effect of the same pharmacological treatment. The two lowest WAY 161503 doses selectively reduced open-arm exploration and increased risk-assessment without affecting locomotor activity. This selective anxiogenic-like effect was observed in both the first and second EPM exposures. The highest WAY 161503 dose produced robust locomotor impairment. In the FST, the same WAY 161503 doses significantly increased the latency to the first immobility in the test session, a behavioral profile that suggests an antidepressant-like action. These results further support the involvement of 5-HT2C receptors in the mediation of anxiety and suggest an intricate relationship between anxiogenic- and antidepressant-like actions