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Aims: Hydroalcoholic T. dodoneifolius, B.pinnatum and T. catappa leaf extracts were investigated for their acute toxicity and anxiolytic activities. Study Design: Acute toxicity (LD50) was determined using the limit dose acute and Anxiolytic activities were assessed by open-field field behavioural testing in mice. Place and Duration of Study: The study took place in the Neurobehavioural room of Department of Pharmacology & Therapeutics, Faculty of Pharmacy, Ahmadu Bello University, Zaria in late December 2022. Methodology: Groups of mice (n=6; equal sexes) were each exposed to the open-field paradigm (OFT) following 1 hour of single oral administration of distilled water, extracts (125, 250, and 500 mg/kg) and diazepam (0. 5 mg/kg) using the behavioural indices of mean centre zone time (M%CZT), centre zone re-entry (MCZR) and defeaction/urination frequency (MD/UF). Results: Acute toxicity testing shows that the three extracts are safe with LD50 of 5g/kg. Behavioural results indicate, compared to the distilled water treatment (M%CZT, 6.39±1.53; MCZR, 4.67±1.15, & MU/UF, 4.83±0.75), single acute T. dodoneifolius (M%CZT, 7.50±1.73, 13.72±2.43, & 20.94±3.91*; MCZR, 7.33±0.88, 9.50±0.76, & 11.50±1.6*; MD/UF, 4.17±0.48, 3.17±0.54, & 1.83±0.60*), and B.pinnatum (M%CZT, 9.72±1.91, 9.78±1.32, & 19.67±2.01*; MCZR, 6.00±1.15, 10.50±0.76, & 12.50±1.72*; MD/UF, 3.17±0.79, 2.33±0.42, & 1.33±0.49*) extract treatments demonstrated consistent dose-dependency in their anxiolytic activity across the three parameters with T. catappa extract (M%CZT, 6.95±1.27, 12.17±2.01, & 16.84±1.49*; MCZR, 8.17±1.60, 10.17±1.67, & 10.83±1.96; MD/UF, 2.83±0.60, 2.00±0.73, & 3.67±0.42) exhibiting dose-pendent anxiolytic effect only on the M%CZT. However, at the highest dose level of 500 mg/kg, all plant extract treatments caused anxiolytic effects that are comparable with those of 0.5 mg/kg diazepam treatments (M%CZT, 22.61±1.31*; MCZR, 12.17±1.66*; & MD/UF, 2.62±0.21*).                                                                                                                   Conclusion: These findings justify the traditional use of these medicinal plant extracts in the remediation of nervous and related disorders.

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The high prevalence and disease burden of anxiety disorders against the paucity and liabilities of existing anxiolytics indicates a need for the discovery of additional/new anti-anxiety agents. However, it is necessary to further screen these new/putative anxiolytic compounds/extracts to rule out the unwanted neurobehavioural toxicities inherent in the existing anti-anxiety drugs. Aqueous methanol leaf extract of Tapinanthus globiferus growing on Azadirachta indica host tree has previously demonstrated significant (p<0.05) anxiolytic effects in mice. This study, therefore, set out to counter-screen this extract for locomotion-suppressant, acute amnesic, sedative (myorelaxant) and hypnotic effects using standard mouse behavioural and biochemical paradigms. The leaf extract (150, 500 and 1500 mg/kg) did not cause significant (p>0.05) alterations in spontaneous locomotor activity, motor coordination/balance, sleep onset or duration, but dose-dependent and significant (p<0.05) increases (63.28±5.63, 65.63±4.12 and 69.18±3.69) in novel object recognition indices of extract-treated compared to 51.54±4.03 and 61.06±2.91 scores in diazepam- and aqua-treated mice, respectively. These findings indicate the aqueous methanol leaf extract is mostly devoid of the evaluated neurobehavioural toxicities and may possess short-term memory enhancement property in mice. These findings may justify the traditional use of Tapinanthus globiferus extracts for memory enhancement.

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