Abstract
Tremor is a common movement disorders and manifested as various diseases such as essential tremor, Parkinsonian tremor and drug-induced tremor. We previously demonstrated that nicotine elicited kinetic tremor by elevating neural activity of the inferior olive which is a potential causal site of essential tremor (PLoS one 10, e0123529, 2015), implying that nicotine may share common mechanisms to essential tremor in inducing kinetic tremor. Here, to clarify the pharmacological characteristics of nicotine-induced tremor, we investigated the effects of various anti-tremor agents on nicotine-induced tremor in mice. Male ddY mice were treated with nicotine (1 mg/kg, i.p.), and the intensity and duration of nicotine-induced tremor was evaluated over 10 min. Anti-essential tremor agents were given 15 min before the nicotine injection. The medications for human essential tremor, propranolol (a β receptor antagonist), diazepam (benzodiazepine receptor agonist) and phenobarbital (a GABAA receptor stimulant), all significantly reduced the duration and intensity of nicotine-induced tremor. In contrast, neither medication for parkinsonian tremor, trihexyphenidyl (a muscarinic receptor antagonist), L-DOPA (a dopamine precursor) nor bromocriptine (a D2 receptor agonist) affected nicotine-induced tremor. These results show that nicotine-induced tremor mimics essential tremor not only for the causative site (inferior olive), but also for the responses to anti-tremor agents, suggesting both tremor types share the common tremorgenic mechanisms.