Lippia multiflora (L.m.) is a verbenacea used in Congo as conventional tea decoction. No traditional indication is known in this country. Nevertheless, in Ghana the plant is used for the treatment of arterial hypertension. The aim of this study is to investigate the psychotropic activity of the aqueous extract of L.m. using the classical tests of experimental psychopharmacology. The extract of L.m. is constituted by lyophilisated powder obtained from an infusion of dried leaves. Different doses are prepared: 200, 400, 600, 800, 1,000 and 1,200 mg/kg dissolved in 1 ml of NaCl 0.9%. L.m. is administered by intraperitoneal or oral route. The wistar rats of both sexes, weighing between 150-200 g, are used. Animal's behaviour is observed macroscopically. The spontaneous motor activity is appreciated by using the number of squares crossed by animal with the four paws in ten minutes (Martin and al. method slightly modified). The rectal temperature is measured. The effect of L.m. on stereotypies induced by apomorphin and anesthesia induced by phenobarbital are studied. The traction test is used to investigate the muscle relaxant effect of L.m. and analgesic activity is evaluated by using acetic acid and hot plate methods by comparison with diazepam 2 and 4 mg/kg. Fischer-t test is used for the statistical analysis of results. L.m. is well tolerated by rats. No mortality is observed with the doses used. So the doses of 200, 400 and 600 mg/kg were selected for experiments. At theses doses L.m. caused: a precocious ataxia, a sedation, a ptosis and a yellow coloration of urines, these effects are dose dependent; a significant reduction of spontaneous motor activity: control 61.60 +/- 6.48, L.m. 200: 16.40 +/- 5.68 (P < 0.01), L.m. 400: 12.20 +/- 2.01 and L.m. 600: 9.60 +/- 1.90 (P < 0.01); no modification of rectal temperature and apomorphin stereotypies; a reduction of sleep latence: control 22.40 +/- 1.89 min, L.m. 200: 17.20 +/- 2.74 min (P < 0.01), L.m. 400: 13.80 +/- 1.81 min (P < 0.01) and L.m. 600: 13.40 +/- 2.16 min (P < 0.01); a potentiation of phenobarbital anesthesia: L.m. 200: 209.80 +/- 29.58 min (N.S.), L.m. 400: 336.40 +/- 22.23 min (P < 0.01), L.m. 600: 342.20 +/- 16.28 min (P < 0.01) and control: 199.40 +/- 2.90 min; an increase at the dose of 400 mg/kg of the time necessary for the restoration of the paws to the metallic bar in the traction test: control; 0.8 +/- 0.1 s, L.m. 400: 7.04 +/- 2.29 s (P < 0.05); a reduction of abdominal cramps induced by acetic acid. This number is respectively 18.40 +/- 4.49 (P < 0.05); 15.00 +/- 2.90 (P < 0.01), 14.20 +/- 3.89 (P < 0.01), 11.60 +/- 4.75 (P < 0.01), 13.00 +/- 2.00 (P < 0.01) and 33.80 +/- 5.04 for L.m. 200 mg/kg, L.m. 400 mg/kg, L.m. 600 mg/kg, Diazepam 2 and 4 mg/kg and control; an increase of reaction time on the hot plate: L.m. 200: 3.26 +/- 0.46 s (N.S.), L.m. 400: 4.50 +/- 0.80 s (P < 0.01), L.m. 600: 10.50 +/- 1.56 s (P < 0.001), diazepam 2 mg/kg: 2.90 +/- 0.51 s (N.S.), diazepam 4 mg/kg: 5.90 +/- 1.09 s (P < 0.01) and control 2.10 +/- 0.26 s. Those results demonstrated that L.m. possess a tranquilizer and analgesic activities as Diazepam. But, anticonvulsant and anxiolytic tests are necessary to confirm the psychopharmacological profile of this medicinal plant.

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