Anxiolytic- and antidepressant-like activities of hydroethanol leaf extract of Newbouldia laevis (P.Beauv.) Seem. (Bignoniaceae) in mice

Abstract

Ethnopharmacological relevance

Newbouldia laevis (Bignoniaceae) is a woody tropical plant commonly found in southwest Nigeria. Ethnobotanical survey and literature revealed its application in the management of CNS disorders e.g. psychosis, insomnia, convulsions and associated anxiety and depression. This study evaluated the anxiolytic and antidepressant activities of the hydroethanol leaf extract of N. laevis in mice.

Materials and methods

The hole-board (HBT), elevated plus maze (EPMT), light/dark exploration (LDET), open field (OFT), social interaction (SIT) (anxiolytic activity), forced swim (FST) and tail suspension (TST) (antidepressant property) tests were employed in this investigation. Mice randomly allotted to different groups were treated orally with distilled water (10 ml/kg), diazepam (1 and 3 mg/kg), imipramine (20 mg/kg) and N. laevis (25–200 mg/kg). The mice were subjected to the various tests 60 min post-treatment.

Results

In the HBT, N. laevis (25 and 100 mg/kg) increased the number of sectional crossings significantly (p < 0.05). In the OFT, N. laevis (25–200 mg/kg) increased the number of general square crossings, centre square crossings, rearings and assisted rearings (p < 0.05). In the EPMT, the extract (25 and 50 mg/kg) increased the open arms time spent, number of head dips and entry (p < 0.05). In the LDET, N. laevis increased the number of transitions at 100 and 200 mg/kg (p < 0.05). For the SIT, N. laevis (25 and 200 mg/kg) increased the frequency and duration of interaction respectively (p < 0.05). In the FST and TST, N. laevis (25–200 mg/kg) increased the latency and reduced the total duration of immobility (p < 0.05). The effect of the extract on duration of immobility was significantly reversed by sulpiride (Dopamine D₂ receptor antagonist).

Conclusion

The hydroethanol leaf extract of N. laevis possesses anxiolytic- and antidepressant-like activities, the later possibly mediated by dopaminergic enhancement(s).

Introduction

From ancient times till date, herbal medicine has been a major practice across the globe, notably in most African and Asian countries where the values of traditional medicinal plants are highly appreciated. Though, orthodox medicines remain at the fore front, plants still make tremendous contributions to human health care; some of these plants identified as medicinal by traditionalists have shown enormous healing powers (Barett et al., 1999). In Africa and Nigeria in particular, a wide range of plants are of great medicinal and nutritional benefits. Against this background, there has been a sustained drive by researchers towards the discovery of new therapeutic agents/drugs with better efficacy and fewer untoward effects compared to the presently available drugs. The therapeutic values of ethnobotanicals have been associated with the presence of diverse phytochemicals (Akinmoladun et al., 2007).

Depression, anxiety, sleep disorders, convulsion and other central nervous system (CNS) disorders represent part of the greatest threats to public health (Alavijeh and Palmer, 2006). The global burden of diseases (GBD) in conjunction with WHO reported neurological disorders as one of the alarming health challenges which has been on the increase worldwide (Murray and Lopez, 1996). Unless drastic actions are taken globally, the scourge of neurological diseases is expected to be even more serious and worrisome. There are several gaps in appreciating the numerous issues related to these disorders and one of them is that neurological services and resources are disproportionately inadequate, especially in low income and developing countries. Against this backdrop, there is renewed impetus in recent years with the sole ambition of coming up with new curative agents for CNS related diseases. In our recent history, researchers are now beaming their searchlights on local products, with a view to developing novel and standardized natural product remedies, especially from plants, with greater efficacy and reduced toxicity to cope with the need of health challenges of mankind, including CNS disorders.

Newbouldia laevis (P.Beauv.) Seem. ex Bureau (Bignoniaceae) is a woody medium sized angiosperm. It is one of the plants with immense value in Africa, especially in Nigeria. Local names in the country include “Aduruku” (Hausa), “Ogilisi” (Igbo), “Akoko” (Yoruba), “Ogiriki” (Urhobo) and “Ikhimi” in Edo. It is commonly called ‘African Border Tree’ and ‘Fertility Tree’ in Nigeria. In Nigeria, N. laevis is used for the management of gastrointestinal disorders (dysentery, pile and constipation), syphilis, rheumatic swelling and elephantiasis (Usman and Osuji, 2007). Ethnobotanical survey and literature revealed its use in the treatment of CNS disorders, including psychosis, insomnia, epilepsy and convulsions (Burkill, 1985; Odugbemi, 2008; Ior et al., 2017). It has been reported that anxiety and depression are common psychiatric symptoms in patients with epilepsy (Kimiskidis et al., 2007) and that epilepsy, anxiety and depression are common disorders which coexist in significant number of patients (Jackson and Turkington, 2005). It has also been reported that anxiety and depression may act as mediating factors in the association between sleep problems and psychotic symptoms (Freeman et al., 2009, 2010; Koyanagi and Stickley, 2015).

Based on ethnobotanical findings, traditional uses and related associations, this study was designed to evaluate the anxiolytic and antidepressant actions of the hydroethanol leaf extract of N. laevis in mice.