Medicinal Herbs and Epilepsy: A Two Edged Sword

Epilepsy is one of the most serious neurological disorders affecting about 0.5-1% of the world population. There is no definite radical therapy against epilepsy; however, actual therapy includes simple inhibition of epileptic activity. Apart from effective drugs against epilepsy, plant extracts as well as essential oils, which have been used for generations by humans to treat the disease, are considered nowadays as potential bioactive agents that can interfere and alter cellular physiological processes involved in epileptogenesis. However, the exact underlying mechanisms and the electrophysiological consequences of action of most medicinal herbs are still not known. Recently, we have reported that the essential oil of Anise, Pimpinella anisum L. (Apiaceae), which is one of the oldest known and highly used spice plants in the folk medicine, causes hyperexcitability at the cellular level and changes the neuronal firing pattern from a regular tonic discharge to an irregular and then to bursting mode in normal cells or potentiates the burst firing and the steepness of the paroxysmal shift induced by PTZ treatment (Janahmadi et al., 2008). However, we have also shown that some herbs, including Cuminum cyminum (Janahmadi et al, 2006) and Artemisia drancunculus (Farajnia et al., 2011), can inhibit the epileptiform activity induced by PTZ, a well known convulsant agent. This sort of contradictory effect of herbal essential oils and extracts is one reason why a certain caution is needed when medicinal herbs are used to treat patients suffering from epilepsy. The present work is focused on comparison of the electrophysiological consequences of essential oil and extract of Tarragon on PTZ-induced neuronal hyperexcitability in snail for the first time. In addition, the effect of anethole, the chief ingredient of many aromatic herbs, including anise and tarragon, on normal neuronal excitability is also tested. Tarragon or dragon's-wort (Artemisia dracunculus) is a perennial herb in the family Asteraceae related to wormwood that exerts radical-scavenging activities (Parejo et al., 2002), antifungal and antitumor effects (Zani et al., 1991; Meepagala et al., 2002) and antiepileptic activities (Sayyah et al., 2004; Farajnia et al., 2011). In Iranian traditional medicine, the dried aerial parts of this plant were mentioned as a treatment for epilepsy (Aqili Khorasani, 1992). The composition of the essential oil of Iranian A. dracunculus was reported to include trans-anethole and α-trans-ocimene as the major constituents (21.1% and 20.6%, respectively). More recently, we demonstrated the dual effects of anethole on Ca2+dependent excitability in snail neurons: at low concentration anethole caused a significant