Evidence for the involvement of the monoaminergic system in the antidepressant-like activity of methanolic extract of Bacopa monnieri in albino mice

Shweta Oommen, Raj Vishnu


Background: Depression is a common illness worldwide, with an estimated 121 million people affected. The efficacy of currently available drugs for treating depression often lack consistency and many of them exert undesirable side effects. This emphasises on the need for newer drugs for the treatment of major depression.

Methods: The present study evaluated the antidepressant-like activity of methanolic extract of Bacopa monnieri in mouse forced swimming test (FST) and tail suspension test (TST), which are predictive models of antidepressant activity. An attempt was also made to understand the involvement of the monoaminergic system and the opioid system in Bacopas’ antidepressant activity. Albino mice were treated with vehicle, fluoxetine (20 mg/kg), or Bacopa monnieri (20, 40, 80, and 120 mg/kg) orally and evaluated in FST and TST. The actophotometer performance was also examined after different treatments. For understanding the mechanisms, different receptor antagonists were used.

Results: Bacopa monnieri produced a significant reduction in the duration of immobility, with better activity at 80 mg/kg dose. Furthermore, the antidepressant-like action produced by Bacopa monnieri was abolished by the pre-treatment of mice with p-chlorophenylalanine (100 mg/kg, i.p., a serotonin synthesis inhibitor), pindolol (10 mg/kg, i.p., a β-adrenoceptor blocker/5HT1A/1B receptor antagonist, ketanserin (5 mg/kg, i.p., a 5HT2A/2B receptor antagonist), prazosin (1 mg/kg, i.p., an α1-adrenoceptor antagonist), and yohimbine (1 mg/kg, i.p., an α2-adrenoceptor antagonist), but not with ondansetron (1 mg/kg, i.p., a 5HT3 receptor antagonist) and naloxone (1 mg/kg, i.p., an opioid receptor antagonist).

Conclusions: These findings suggest that the antidepressant-like effect produced by Bacopa monnieri may be mediated through an interaction with the serotonergic and noradrenergic nervous system. The antidepressant doses of Bacopa monnieri had no effect on the locomotor activity of mice.


Antidepressant-like effect, Bacopa monnieri, Mice, Noradrenergic, Serotonin, Tail suspension test

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