Antidepressant-like effects of methanolic extract of Bacopa monniera in mice

Depression is the second leading psychiatric disorder where 21 % of the world population suffers from this disease [1]. The age range is markedly decreasing from 40–50 years age range to 25–35 years age range which observed worldwide [2]. In last few decades, several drugs have been discovered to treat depression such as tricyclic antidepressants, monoamine oxidase inhibitors [3] and selective serotonin reuptake inhibitors (SSRI). But unfortunately, all of the drugs have serious side effects including insomnia, anxiety, weight gain etc. It is well known that nature is the best and safe source for all medicine. So it becomes worth to search for a new antidepressant drug from natural source with less side effects (It is assume that a drug from natural source could have less side effects) and complications [4].

Bacopa monniera (Family: Scrophulariaceae), commonly known as Brahmi, is an aquatic herbs distributed throughout the warmer regions of the world including Bangladesh. It grows in wet, damp, marshy areas and possesses a wide range of medicinal values including memory enhancement, improvement of cognitive disorders, focusing and alertness as well as reduces anxiety [5, 6]. In Bangladesh, this plant is extensively used in the traditional medicine system as potent therapeutic agent as a neurological tonic to enhance intellectual development [7], to treat epilepsy [8], cardiac [9], respiratory [10] and digestive [11] disorders, toothache and purifies blood. In some parts of this country Brahmi is used to treat rheumatism and to prevent miscarriage [12]. Conversely, B. monniera is associated with gastrointestinal side-effects, specifically increased bowel movements, nausea, and abdominal cramping [13]. Toxicology studies of the extract used in the current study—BacoMind,™—have not shown gastrointestinal reactions in rats [14] and safety and tolerability studies of BacoMind™ in human volunteers reported only mild gastrointestinal reactions in 3 of 23 participants that subsided instinctively. Possibly the higher incidence of gastrointestinal reactions in the current study was due to the older age of participants, lowering their capacity to tolerate Bacopa [13]. There are several reports revealing that Brahmi contains flavonoids [15], alkaloids, glycosides, saponins and sterols [16]. Some researchers isolated some of these phytochemicals such as Brahmin, nicotine, herpestine, des-saponin glycosides-triterpenoid saponins like Bacosides A & B. It has been found that the phytochemicals like 3-(a-L-arabinopyranosyl)-O-b-D-glucopyranoside-10 and 20-dihydroxy-16-keto-dammar-24-ene (Bacosides A & B) are the major compounds that may exhibit neuropharmacological activities by directly acting on the neurotransmeter’s level [17, 18]. The other chemical constituents reported for this plant includes A1 & A3 [19, 20], hersaponin [21], betulic acid, monnierin [22], herpestin and brahmine [23], luteolin-7-glucoside, glucoronyl-7-apigenin and gluucoronyl-7-luteonin, common phytosteroids [7]. Due to the diverse pharmacological actions of Brahmi, research tried to investigate and validate its ethnomedical uses based on the advanced research techniques. They found Brahmi as a potent agent with antioxidant [24], antiulcerogenic [25], cognitive enhancer [26], anti-inflammatory, anxiolytic [27], analgesic, antipyretic, and sedative [26] properties. However, the neuropharmacological activity of this plant is not investigated extensively which influenced us to design our study. The present study investigated the antidepressant-like effect of MEBM in different behavioral model of depression in mice.

The methanolic extract of B. monniera showed antidepressant-like effects in prophetic animal models, namely forced swimming, measurement of locomotor activity and tail suspension tests. MEBM (50, 100 and 200 mg/kg body weight) or the synthetic antidepressant drug, Imipramine hydrochloride (30 mg/kg), was orally administered to the mice once daily for 14d. There was no difference in body weight gains after 14d among test treatment groups (Table 1). The extract (50, 100 and 200 mg/kg body weight) significantly reduced the duration of immobility time in the forced swimming test after 14d daily treatment (Table 2 and Fig. 1). Dunnett’s post hoc analysis demonstrated that the test treatments significantly decreased the immobility time in comparison to the control group (p < 0.001). Likewise, the extract reduced the duration of immobility time in the tail suspension test (Table 3 and Fig. 2). Post hoc analysis confirmed that the extract significantly decreased the immobility time in comparison to the control group (p < 0.001).

The effectiveness of the decreasing immobility in the FST was also shown previously with psycho stimulants, which exert an indiscriminate motor stimulating activity. For this false positive result, we employed an additional measurement of locomotor activity test to check the motor stimulating activity of the MEBM. Administration of the extract of B. monniera at doses of 50, 100 and 200 mg/kg for 14 days, active doses in the FST, resulted in no behavioral changes or motor dysfunction in the measurement of locomotor activity test (Table 4 and Figs. 3, 4 and 5).

As shown in Fig. 3, MEBM (50 and 200 mg/kg) was shown the satisfactory locomotion effect. At the doses of 100 and 200 mg/kg was significantly augmented the good rearing effect of this test (Fig. 4). Extracts of B. monniera (100 and 200 mg/kg) was shown good effect of defecation phase (Fig. 5). Moreover, Post hoc analysis also verified that the extract significantly increased the locomotion, rearing and defecation effects in comparison to the control group (p < 0.001).

The purpose of this study was assessed the antidepressant-like effect of MEBM using animal behavioral models. A major problem in the screening for new antidepressant effect is the establishment of a valid animal model able to sufficiently and accurately identified diverse depressant treatments, without making errors of omission [35]. In that case, the forced swimming and tail suspension tests are widely accepted behavioral models for the assessment of antidepressant activity. The characteristic behavior evaluated in these tests, termed immobility, has been considered to reflect behavioral despair similar to that seen in human depression, and it is well known that antidepressant drugs are able to reduce the immobility time in rodents [30]. It is interesting to note that the immobility shown by mice when subjected to unavoidable stress such as forced swimming test is thought to reflect a state of despair or lowered mood, which is thought to reflect depressive disorders in humans. In addition, the immobility time is reduced by treatment with antidepressant drugs [36]. There is a significant correlation between the clinical efficacy of antidepressant drugs and their potency in the FST, this was not found in any other model [34, 36]. Interestingly, our data indicate that higher doses of plant extracts were more effective than smaller doses both in forced swimming and tail suspension tests.

Based on our present study, antidepressant-like effect of MEBM in all the classic models of depressants, where it was found to possess antidepressant-like activity comparable to the standard drug Imipramine hydrochloride. Imipramine hydrochloride acts by inhibiting norepinephrine (NE) reuptake and has been used as a standard drug in majority studies. The beneficial effect of Imipramine hydrochloride in the forced swimming test model seems to be due to increased availability of these neurotransmitters (NE) and serotonin (5HT) at the post synaptic site following reuptake inhibition [37].

Initial hypothesis of depression has been formulated about 40 years ago, proposing that the main symptoms of depression due to functional deficiency of cerebral monoaminergic transmitters such as (NE), 5HT, and dopamine (DA) located at synapses [38]. Some studies have also shown the adaptogenic effect of the plant extract via normalization of the various stress parameters and monoaminergic levels which may provide a clue that the extract is bringing their possible antidepressant-like effect through restoration of normal monoaminergic neurotransmitters [39].

Brahmi contains a natural phytonutrients which is known as bacosides. This is responsible for improving vital neurotransmitters activities which happen in memorization and information process and may be helpful in depression [40]. The action of the triterpinoid saponins and the bacosides A and B has resulted in the enhancement of the nerve impulse transmission. Neurochemical assays suggested that treatment by bacosides or bacopasides I improved brain antioxidant activity to varying degrees after the behavioral despair test. These findings indicated that the antidepressant-like effect of bacopasides I might be related to both antioxidant activation and noradrenergic activation [41]. Three new triterpene glycosides, bacopasides VI-VIII, together with three known analogues, bacopaside I (1) , bacopaside II (2) and bacopa saponsin C (3), were isolated from the whole plant of B. monniera. Compounds 1, 2 and 3 were shown antidepressant activity when tested on forced swimming and tail suspension in mice, respectively [42].

Recently, oxidative stress was linked with the pathophysiology of major depression, with significant correlations being found between the severity of depression and erythrocyte superoxide dismutase/lipoperoxidation levels [43]. Meanwhile, treatment with antidepressants reduces the oxidative stress related to depressive disorder [44, 45]. Additionally, some species such as Bacopa monneira, Withania somnifera and Asparagus racemosus, all of which are reported to have antidepressant-like properties, also possess antioxidant activity [46‐48]. Therefore , it is possible that the antioxidant activity of the methanol extract from B. monniera may contribute to its antidepressant-like effect. However, different kinds of the research study must needed to elucidate the mechanism of action of B. monniera in the CNS, the pattern of effects were observed in these experiments suggest the involvement of the norepinephrine neurotransmitters system on its antidepressant-like effects.

In the present investigation, we have reported antidepressant-like effect of MEBM in all the classic models such as forced swimming test (FST), measurement of locomotor activity test (MLAT) and tail suspension test (TST), where it was found to possess significant antidepressant-like activity comparable to the standard drug Imipramine hydrochloride. Different kinds of the research study must needed to elucidate the mechanism of action of B. monniera in the CNS, the pattern of effects were observed in these experiments suggest the involvement of norepinephrine neurotransmitters system on its antidepressant-like effect. The present study also warrants further investigation into identification of the active compounds in herbal medicines, in particular extract of B. monniera with antidepressant-like effects.