Pharmacology Biochemistry and Behavior, Vol. 65, No. 1, pp. 117–121, 2000 © 1999 Elsevier Science Inc. Printed in the USA. All rights reserved 0091-3057/00/$–see front matter PII S0091-3057(99)00175-6 117 Effect of Lidocaine on Harmaline-Induced Tremors in the Rat N. BIARY, M. ARSHADUDDIN, S. AL DEEB, K. AL MOUTAERY AND M. TARIQ Neuroscience Research Group, Armed Forces Hospital, Riyadh, Saudi Arabia Received 11 December 1998; Revised 24 May 1999; Accepted 4 June 1999 BIARY, N., M. ARSHADUDDIN, S. AL DEEB, K. AL MOUTAERY AND M. TARIQ. Effect of lidocaine on harmaline-induced tremors in the rat. PHARMACOL BIOCHEM BEHAV 65(1) 117–121, 2000.—The present study was un- dertaken to investigate the effect of lidocaine on harmaline-induced tremors in the rat. Four groups of Wistar rats weighing 45–50 g were injected with harmaline (50 mg/kg IP) for inducing experimental tremors. The rats in group 1 served as control, whereas the animals in groups 2, 3, and 4 were also given lidocaine IP at doses of 12.5, 25, and 50 mg/kg, respectively, 10 min after the onset of tremors (therapeutic study). In a separate four groups of animals intraperitoneal lidocaine injection was given 10 min before harmaline (prophylactic study) in the same dose regimen as mentioned above. The latency of onset, in- tensity, and duration of tremor and electromyographic responses were recorded. Lidocaine dose dependently attenuated har- maline-induced tremors in rats. The latency period was increased, and duration and intensity of harmaline-induced tremors was reduced by lidocaine. Our electromyography (EMG) study also revealed a decrease in the amplitude of harmaline- induced tremors in lidocaine-treated rats. In conclusion, the results of this study clearly suggest beneficial effects of lidocaine in harmaline-induced tremors. © 1999 Elsevier Science Inc. Harmaline Tremors Lidocaine EMG ESSENTIAL tremors are a monosymptomatic illness with a reported prevalence of 4 to 60 per thousand people (4,10). The prevalence of essential tremors increases with advancing age, but it is fairly common in all age groups, and almost equal in men and women (26). Essential tremors commonly affect the head and neck and upper extremities; however, tremors of the trunk and lower extremities is also observed in some pa- tients. The patients usually seek medical attention because of functional disability and social embarrassment. According to Holmes (14), tremors is the least understood symptom in neu- rology, and even after almost a century this statement largely holds true. Essential tremors result from both physiologic and pathologic processes in the nervous system, and always in- volve the interaction of central and peripheral nervous sys- tems. Owing to a lack of understanding of the basic mecha- nism and origin of tremors, it has been difficult to develop pharmacological agents with selective and specific antitremor activity. Experimental studies using animal models have provided considerable insight into the etiology, mechanism, and phar- macology of essential tremors. Harmaline, a tremorogenic al- kaloid produces tremors resembling centrally induced tremors (30), which provides a close model for postural tremors (9). Postural tremors result from synchronous olivary discharge, which tend to fire rhythmically due to alternating period of membrane hyperpolarization and rebound depolarization (3,17,19). Harmaline causes inferior olive neurons to fire syn- chronously and to act as a pacemaker for the generation of tremor (20), which spreads to other areas of the brain (2). Moreover, like essential tremors, harmaline-induced tremors are also suppressed by propanolol (1), diazepam (5), barbitu- rates (16), and ethanol (29), further confirming that harmaline shares the pharmacological properties of essential tremors. Topical anesthesia has been successfully used to suppress tremor amplitude and the associated electrical activity in per- sons with essential tremors (25). Lidocaine is widely used as a Requests for reprints should be addressed to Mohammad Tariq, Ph.D., FRCPath., FRSC., Consultant and Head, Research Center, Armed Forces Hospital, P.O. Box 7897 (W-912), Riyadh 11159, Saudi Arabia.