Civilizations throughout the world have been using plants as medicines for thousands of years and continue to do so today. In centuries before the advent of modern medicine, synthetic chemistry and the pharmaceutical industry, virtually all medicines came from plants (Agosta, 1997). These medicinal plants have been an important source for the discovery of novel bioactive compounds which served and continue to serve as lead molecules for the development of new drugs (Cragg et al., 1997). Aspirin, atropine, codeine, digoxin, morphine, pilocarpine, pseudoephedrine, guanine, scopolamine, taxol, theophyline, tubocurarine, vincristine and vinblastine, are examples of such invaluable therapeutic tools for today’s physicians (Jones, 1996, Cox and Balick, 1994, Phillipson and Anderson, 1989). Even in modern era of science and discoveries, 80% of the world population chiefly relies on traditional medicines for their primary health care needs (Akerele, 1993)
Epilepsy is one of the major neurological disorders where modern drug therapy is complicated by side-effects, teratogenic effects, long-term toxicity ad about 40% patients are refractory to therapeutic intervention and thus its effective and safe therapy remains a challenge (SamrJn, et al., 1997, Mattson, 1995, Devinsky, 1995, Holmes, 1993, Smith and Bleck, 1991). All the currently available antiepileptic drugs are synthetic molecules. Medicinal plants used for the therapy of epilepsy in traditional medicine have been shown to possess promising anticonvlsant activities in animal models of anticonvulsant screening (vide appendix) can be an invaluable source for search of new antiepileptic compounds.
The present report is an investigation of anticonvulsant activities of some indigenous medicinal plants used for the treatment of epilepsy by traditional healers in Karachi, Pakistan. We selected three medicinal plants on the basis of interviews of healers and folk and scientific literature search. The ethanolic extracts of these plants were subjected to acute toxicity and than screened for anticonvulsant activities on Maximal Electroshock (MEST) and subcutaneous Pentylenetetrazole (scPTZ) Tests in mice. One of these plants, Delphinium denudatum exhibited depressant effects on behaviour and significant anticonvulsant activity. It was further fractionated and screened for anticonvulsant activity in subcutaneous Bicuculline (scBIC), Picrotoxin (scPTX) and Strychnine (scSTN) tests.
The mechanism of in vivo anticonvulsant actions of aqueous fraction and its subfractions isolated from Delphinium denudatum was explored by whole cell current clamp studies to investigate their effects on Sustained Repetitive Firing (SRF) (Macdonald, et al., 1985) of hippocampal neurons in culture. We further studied the effects of aqueous fraction and its most active FS-1 sb-fraction for PTZ, BIC and PTX-induced epileptiform activity in hippocampal nerons. Voltage clamp studies were carried out on purified subfraction FSS 15-19 which comprised of two novel compounds delphadione I and II, for their effects on GABA, receptor mediated miniature Inhibitory Post Synaptic Currents (mlPSCs) (Soltesz et al., 1995) and GABA evoked responses (Gibbs III et al., 1997) in hippocampal neurons
From the results of these studies it can be stated that aqueous fraction and its sub-fraction FS-1 contains bioactive compounds with significant anticonvulsant activities in MEST, scPTZ and scBIC tests in mice. Moreover these compounds inhibited SRF of rat hippocampal neurons in culture and PTZ, BIC and PTX induced epileptiform activity in hippocampal neurons was also suppressed. However, the studies on FSS 15-19 (delpadione I and II) did not reveal any significant effects o GABAA receptor-mediated mlPSCs and GABA-evoked responses.
At present we are of view that one of the mechanism(s) of action of anticonvulsant compounds present in Delphinium denudatum is dose-dependent, use-dependent and voltage-dependent block of SRF, possibly by interaction with sodium channels. Results of some experiments with SRF also suggest that the site of action of these compounds is accessible only through extracellular site of the sodium channel. Results also do not exclude the possibility of presence of other bioactive compounds in fraction FS-1 which may have different mechanism of anticonvulsant action.