Neurobehioural Effects of Chronic Consumption of Uncooked Black Eye Beans on Spatial Learning and Memory in Mice

Beans, the stable diet of Nigerians contains serotonin and its precursor, 5-Hydroxytryptophan. Serotonin as a neurotransmitter has neurobehavioural actions which include mood, memory, learning and sleep. It was therefore the aim of this study to find out whether long term consumption of uncooked black eye beans (Vigna unguiculata) diet commonly called iron beans, has effects on some neurobehavioural parameters notably; learning and memory, using Swiss white mice as experimental animals. Thirty (30) CD1 mice weighing 18-30g were randomly assigned into three groups, viz; control, uncooked beans and serotonin precursor. They were fed normal rodent chow and 50% uncooked beans diet (w/w), while another set of mice were placed on serotonin precursor (5-HTP) diet (0.2mg/50g w/w) respectively for four weeks. All the mice had access to clean drinking water ad libitum. Before the neurobehavioural parameters were assessed, the phytochemical analysis of the beans, LD50 of the beans (Vigna unguiculata) and that of the serotonin precursor (5-HTP) were determined. Serotonin concentration was measured in the beans using gas chromatography analysis. Learning and memory, was investigated alongside food and water intake and body weight change. Mice were tested in the Morris water maze for 8 days: 3 days of acquisition training, 3 days of reversal training, 1 day of single probe trial and 1 day for visible platform task. Learning on days 1, 2 & 3 of acquisition training was improved in the uncooked beans and serotonin precursor diet-fed mice when compared to control (p<0.001, respectively). The trend was similar during the reversal training, memory was improved in the beans and serotonin precursor diet-fed mice when compared to control (p<0.001). During the probe trial, the swim duration in the South-East quadrant was significantly higher for uncooked beans and serotonin precursor group compared to control (p<0.05). However, during the visible platform task, the swim latencies for the uncooked beans and serotonin precursor group were significantly lower compared to control. In conclusion, long term consumption of uncooked beans diet enhances cognitive memory and can be therapeutically useful in retrograde amnesia.