The herbal preparations of the root bark of Annona senegalensis Pers (Annonaceae) is used in traditional medicine in South Eastern Nigeria for the treatment of epilepsy and febrile convulsions. A pilot study has confirmed the potency of the root bark of A. senegalensis in the control of seizure in mice. The current study was aimed to identify the active phytochemical responsible for the activity. Activity guided fractionation of the methanol: methylene chloride root bark extract (MME) afforded ethylacetate fraction (EF) as the most anticonvulsant potent fraction between hexane fraction (HF) and methanol fraction (MF) when studied for anticonvulsant activity in mice using pentylenetetrazole (PTZ) (60 mg/kg, s.c.) induced convulsions. Further fractionation of the ethyl acetate fraction (EF) yielded eight (8) fractions of which fraction F4 gave the most potent activity. Phenobarbitone induced sleep time test and motor coordination test on rota-rod performance were also used to assess the sedative and central depressant effects of MME, EF, and F4. Acute toxicity and lethality (LD50) test as well as phytochemical analysis were also performed on the extract and fractions. Results indicated that the MME, EF (200, 400, 800 mg/kg) and fraction F4 (50, 100 and 200 mg/kg) exhibited a dose dependent significant (P < 0.05) delay in the latency of myoclonic spasms and tonic - clonic phase of seizure induced by PTZ. At 200 mg/kg MME, EF and F4 respectively offered 60, 80 and 60 % protection against seizure induced death while HF and MF offered no percentage protection. Also MME, EF and F4 decreased the latency and increased the duration of phenobarbitone induced sleeping time as well as exhibited a significant (P < 0.05) inhibition of motor incoordination. The acute toxicity test revealed an oral LD50 of 1296 and 2154 mg/kg for MME and EF respectively, while the phytochemical studies showed the presence of alkaloids, resins, glycosides, carbohydrate, reducing sugar, fats and oils, flavonoids, and terpenoids. The phytochemical analysis revealed that flavonoids were present in MME, EF and F4 and absent in HF and MF. The results suggested that the extract and fractions of A. senegalensis possessed anticonvulsant activity and central depressant effects which may be attributable to the flavonoids.
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