Anticonvulsant and related neuropharmacological effects of a hydro-ethanolic whole plant extract of synedrella nodiflora (L.) gaertn (FAM:Asteraceae).
Synedrella nodiflora (L.) Gaertn. (Family: Asteraceae) is an annual herb which grows to about 60-120 cm high and occurs throughout the West African region. In Ghanaian traditional medicine, the whole plant is used for the treatment of epilepsy. This study presents the anticonvulsant, sedative, muscle relaxant, antinociceptive, antioxidant, the effect on anxiety and the safety of a hydro-ethanolic extract of the whole plant of Synedrella nodiflora. Four murine models of experimental epilepsy were employed for the anticonvulsant screening of the extract, namely; pentylenetetrazole-, picrotoxin- and pilocarpine- induced seizure and penetylenetetrazole- induced kindling. The ability of the extract to cause sedation was investigated using the pentobarbitone- induced sleep test. The neuromuscular effects of the extract were also determined in vivo using the rota-rod test and in vitro with the chick biventer cervicis preparation. Moreover, formalin induced pain and acetic acid induced writhing assay were the tests employed to assess the antinociceptive effects of the extract. The antioxidant effects of the extract was also determined by measuring the total phenols, antioxidant capacity, 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) scavenging assay, reducing power assay and inhibition of linoleic acid peroxidation. The elevated plus maze, the light/dark test and the Versamax animal monitor were used to investigate the effect of the extract on anxiety in rodents. The acute toxicity test was also done to assess the safety of the extract as herbal medicine. The extract, SNE, showed significant anticonvulsant effect against seizures induced by PTZ by dose dependent increase in both the onset of the myoclonic jerks and latency to myoclonic seizures and a reduction in the duration of seizures. However this effect was not significant compared to the vehicle treated group and not dose dependent. SNE significantly and dose- dependently delayed the latencies to myoclonic jerks and tonic-clonic seizures induced by picrotoxin. SNE also reduced the duration of seizures significantly. SNE also significantly reduced the total frequency of seizures. SNE, also, dose-dependently reduced the total duration of seizures induced by pilocarpine in the mice treated. SNE significantly suppressed the PTZ- kindled seizure at all the dose levels used. SNE (100-1000 mg kg-1) dose-dependently inhibited lipid peroxidation in the PTZ-kindled rats. SNE also, dose-dependently, increased the duration of sleep induced by pentobarbitone in mice. The ability of SNE to attenuate PTZ-, picrotoxin- pilocarpine- induced seizures, PTZ- induced kindling, enhanced sedation of pentobarbitone suggests the possible involvement of GABAergic, anti-cholinergic, or antioxidant mechanism(s). SNE at 1000 mg kg-1 produced a significant reduction in the time spent on the rota-rod at 24 rpm over the two-hour period thus suggesting motor impairment at this dose. Baclofen at 10 mg kg-1 significantly reduced the duration spent by pre-treated mice on the rota-rod. SNE also antagonised acetylcholine- induced contractions in the chick biventer cervicis preparation, thus a neuromuscular blocker. These results suggest a skeletal muscle relaxant effect by S. nodiflora possibly via centrally mediated mechanism(s) involving neuromuscular blockade. In the formalin-induced pain and the acetic acid- induced writhing, morphine and diclofenac were used as standard opioid and NSAID respectively. The hydro-ethanolic extract of S. nodiflora (100-1000 mg kg-1, p.o) and morphine (1-10 mg kg-1) dose-dependently decreased both phases of the formalin-induced nociceptive behavior. The antinociceptive effects of S. nodiflora (300 mg kg-1, p.o) on the first and second phases of formalin-induced pain were significantly blocked by caffeine but not by naloxone. In the acetic acid-induced writhing test, diclofenac and S. nodiflora significantly reduced the number of writhes dose-dependently. Also, the effect of the S. nodiflora (300 mg kg-1) was blocked by caffeine (3 mg kg-1) but the analgesic effect of diclofenac was significantly enhanced. The observed effects of caffeine on the central and peripheral analgesic effects of S. nodiflora in the formalin and acetic acid- induced writhing suggest the possible involvement of adenosinergic mechanism(s). The extract (0.1-3.0 mg ml-1 ) was found to contain phenolic compounds which could be responsible for the antioxidant properties. The extract also exhibited antioxidant properties by reducing Fe3+ to Fe2+ in the reducing power test, scavenged DPPH free radicals and effectively inhibited linoleic acid autoxidation. In the EPM paradigm, S. nodiflora extract (10-300 mg kg-1) exhibited anxiogenic-like activity by dose-dependently decreasing the number of entries into both the open and closed arms, no significant effect on the percent number of entry into the open arms and a decrease in the time spent in the open arm in comparison to the vehicle-treated group. Similarly, S. nodiflora extract (SNE) dose-dependently decreased the number of head dips and stretch-attend postures and the duration of grooming. In the LD test, SNE also exhibited anxiogenic-like effect by significantly and dose-dependently reducing the number of entry into the light compartment, the number of transitions and not significantly, the time spent in the light area. In the EPM and LD test, diazepam (0.1-1.0 mg kg-1), a reference anxiolytic drug, produced a directly opposite response to that exhibited by SNE. The extract, in the VAMS, decreased the locomotor activity of pretreated-mice dose dependently and significantly. SNE reduced the distance travelled and time spent at the center of the observation cage indicating an anxiogenic-like effect. The extract‟s ability to cause a general reduction in locomotor activity suggests sedative effects rather than anxiogenesis. Oral administration of SNE (1000-10,000 mg kg-1) yielded no mortality in the treated mice over a 24 h of observation. Thus the LD50 was approximated to be greater than 10,000 mg kg-1. Thus the extract can be said of as being less toxic. Also high protective indexes produce in the PTZ-, picrotoxin- and pilocarpine-induced seizures by the extract suggest that it has a safe therapeutic profile. In conclusion, the hydro-ethanolic extract of S. nodiflora has anticonvulsant effect in the acute and chronic seizure models of epilepsy used and indicates a possible GABAergic mechanism(s); exhibits central analgesic effect possibly mediated through adenosinergic mechanism and a peripheral anti-inflammatory activity and a potent antioxidant and free radical scavenger, a muscle relaxant and has anxiogenic-like and sedation effects.
A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy on February, 2011.