Piperine decreases pilocarpine-induced convulsions by GABAergic mechanisms

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Abstract

Piperine, an alkaloid present in the Piper genus, was shown to have an anticonvulsant activity, evaluated by the pilocarpine-induced model, in mice. Pilocarpine (350 mg/kg, i.p.) was administered 30 min after piperine (2.5, 5, 10 and 20 mg/kg, i.p.) which significantly increased latencies to 1st convulsion and to death, and percentage of survivals. These parameters were also increased in the pilocarpine groups pretreated with atropine plus piperine (10 and 2.5 mg/kg, respectively), as related to the pilocarpine group. However, they were not altered in the pilocarpine groups pretreated with memantine (a NMDA-type glutamate receptors blocker, 2 mg/kg, p.o.) or nimodipine (a calcium channel blocker, 10 mg/kg, p.o.), both associated with piperine (1 or 2.5 mg/kg), as compared to the piperine plus pilocarpine group. Moreover, the pilocarpine group pretreated with diazepam (which binds to the GABAA receptor, 0.2 and 0.5 mg/kg, i.p.) plus piperine (1 and 2.5 mg/kg) significantly increased latency to the 1st convulsion, as related to the pilocarpine group, suggesting that the GABAergic system is involved with the piperine action. Furthermore, the piperine effect was blocked by flumazenil (2 mg/kg, i.p.), a benzodiazepine antagonist. Untreated P350 animals showed decreased striatal DA and increased DOPAC and HVA levels that were not affected in the piperine plus pilocarpine groups. Piperine increased striatal levels of GABA, glycine and taurine, and reversed pilocarpine-induced increases in nitrite contents in sera and brain. Hippocampi from the untreated pilocarpine group showed an increased number of TNF-α immunostained cells in all areas, as opposed to the pilocarpine group pretreated with piperine. Taken together, piperine anticonvulsant effects are the result of its anti-inflammatory and antioxidant actions, as well as TNF-α reduction. In addition, piperine effects on inhibitory amino acids and on the GABAergic system may certainly contribute to the drug anticonvulsant activity.

Highlights

▸ Piperine is an alkaloid and bioactive constituent of plants from the Piper genus. ▸ It is a potent anticonvulsant drug against pilocarpine-induced convulsions in mice. ▸ Its effects are not altered in the presence of memantine or nimodipine. ▸ Its effects are potentiated by diazepam and blocked by flumazenil. ▸ Its activity involves GABAergic mechanisms and TNF-alpha decreases.

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