The Effect of Thyme (Thymus Capitatus L.) Esential Oil and its Major Constituent Carvacrol on Peripheral Nerve Excitability

Objectives: Essential oils (EO) are known for having neuropharmacological properties such as ansiolitic, analgesic or anticonvulsant, and the monoterpenes, main EO constituents, are considered responsible for its biological effects. Carvacrol is a monoterpene which constitute about 80% of the thyme (Thymus capitatus L.) EO. Therefore, this study proposes to investigate the effects of thyme EO on peripheral nerve excitability and further evaluate carvacrol as its major effective constituent. Methods: The single sucrose gap technique was used to investigate the effects of thyme EO and carvacrol on the compound action potential (CAP) acquired from rat sciatic nerve (Wistar, ~350g). During experimental procedures, fastconducting myelinated fibers (A?) were selectively stimulated by rheobase cronaxy. Thyme EO (500?g/mL) and carvacrol (10mM) were separately incubated for 30 minutes. Subsequently, the nervous trunk was washed out with physiological solution alone (~1mL/min). Eventual changes in amplitude (ACAP), depolarization velocity (Vdep) or the time constant of repolarization (?rep) were analyzed by Student's t-test and posterior normalized from control (n=3-4). Results: Thyme EO reduced 47.7±4.5% of ACAP with only 5 minutes of incubation, reaching maximal effect (92.8±6.3%) after 15 minutes (p<0.05) and completely reversed by 30 minutes of nerve washing. Similarly, carvacrol decreased 51.6±8.7% of ACAP at 5 minutes, and completely blocked CAP conduction after 15 minutes of incubation (p<0.01), although by an irreversible manner. Moreover Vdep was reduced of about 57.7±9.8% and 46.1±10.8%, after 5 minutes of thyme EO and carvacrol, respectively (p<0.05). No significant alterations on ?rep were observed for both drugs. Conclusion: We have demonstrated the effectiveness of Thyme (Thymus capitatus L.) EO in reducing the peripheral nervous e