Neurobehavioural Properties of Lima Bean: Antipsychotic, Anxiolytic, and Sedative–Hypnotic-like Actions in Mice

Psychotic disorder remains a major global health burden despite the plethora of anti-psychotic medications currently available. Poor adherence owing to numerous adverse effects and cost burden is a major challenge to treating psychosis. In view of this, the use of ethnomedicinal plants has become more common. In Nigeria, West Africa, the seeds of Phaseolus lunatus (Lima bean) are used to treat psychosis-like illness. Despite its extensive use, there are not many scientific studies that validate its efficacy. Therefore, this study evaluated the antipsychotic, anxiolytic-like, and sleep-enhancing properties of the seed extract. Pulverized dried seeds were extracted in a mixture (1:1) of water and methanol and screened for phytoconstituents. Using murine models, oral doses of 400, 800, and 1600 mg/kg of the extract were evaluated for antipsychotic, anxiolytic, and sleep-enhancing properties. Brain malondialdehyde (MDA), superoxide dismutase (SOD), catalase, glutathione peroxidase, and glutathione reductase (GR) levels were estimated after administering the doses of extract to mice for 14 consecutive days. The seed extract significantly inhibited d-amphetamine-induced stereotypy and ketamine-induced hyperlocomotion in a dose-dependent manner. It also exhibited significant anxiolytic-like activity at 800 mg/kg, as indicated by increased time spent on the open arm of the elevated plus maze and an increased number of head dips on the hole board. Compared with untreated controls, sleep onset was significantly faster, and sleep duration was longer in mice that received 1600 mg/kg of the extract. There was a decrease in MDA levels at a dose of 1600 mg/kg and an increase in SOD and GR levels in the mice brains. Our findings suggest that Lima bean extract exhibited antipsychotic-like, anxiolytic-like, sedative–hypnotic, and antioxidant activities in mice likely due to its flavonoid and alkaloidal constituents. Our study provides preliminary evidence in mice that supports the ethnomedicinal use of Lima beans as a functional food for psychosis-like illness.