Effects of combined escitalopram and aripiprazole in rats: role of the 5-HT1a receptor.

RATIONALE: Pre-clinical and clinical studies have suggested that the antidepressant efficacy of escitalopram (ESC) can be augmented by co-administration of aripiprazole (ARI).

OBJECTIVE

To establish if the effects of ESC + ARI can be altered by modulating the 5-HT1a receptor.

METHODS

Sprague-Dawley male rats received ESC + ARI (10 and 2 mg/kg/day, respectively, via osmotic or by cumulative injections), as well as the 5-HT1a antagonist WAY-100635 (WAY; 0.01-1 mg/kg) and the 5-HT1a agonist 8-OH-DPAT (DPAT; 0.3-1 mg/kg) prior to testing in locomotion chambers and in the forced swim test (FST). Expression of the 5-HT1a receptor mRNA in the dorsal raphe nucleus, hippocampus, septum, and entorhinal cortex was also assessed.

RESULTS

WAY generally synergized, while DPAT antagonized, the effect of ESC + ARI on motor activity. All groups showed significantly lower 5-HT1a mRNA in the dorsal raphe nucleus. In the hippocampus, ESC + ARI and WAY + ESC + ARI groups displayed equivalent elevations of 5-HT1a mRNA, but this was not observed in groups that received DPAT + ESC + ARI. Finally, the addition of ARI to ESC augmented the effect that ESC alone had on reducing immobility in the FST. Importantly, WAY antagonized this effect, while DPAT had no consequences.

CONCLUSIONS

Taken together, these results in rats indicate that the 5-HT1a receptor is involved in the behavioral and brain region-specific mRNA effects of ESC + ARI.