Quantification of S-adenosylmethionine-induced tremors: a possible tremor model for Parkinson's disease.

Tremor is the most visible symptom of Parkinson's Disease (PD), and should be the appropriate parameter in models for its evaluation. Lack of reliable PD tremor models and methods to distinguish tremors from nontremor movements means that nontremor behavior such as rotation following basal ganglia damage are mostly used. Our laboratory has shown that S-adenosyl-methionine (SAM) injections into the brain of rats reliably produced tremors, rigidity, hypokinesia, and abnormal posture. Thus, SAM-induced tremors, when distinguished from nontremor activities, has the potential as a model for testing anti-PD agents. Tremor Monitor-recorded activity profiles of the rats injected with SAM showed low-amplitude signals interlaced with high-amplitude bursts of tremor episodes. Control activities were of low-medium amplitudes with no such patterns. The number of real and apparent episodes detected over 20 min were 92 +/- 12 and 84 +/- 14 lasting 470 +/- 50 and 210 +/- 50 s, indicating mean durations of 5.1, and 2.4 s, frequencies of 12 +/- 0.1 and 11 +/- 0.2 Hz, cycles (waves) per episode of 54 +/- 6 and 19 +/- 2 and amplitudes of 42.3 +/- 5 and 19.8 +/- 1 for the SAM-treated and control rats, respectively. The nontremor activities of rats injected with phosphate-buffered saline were distinguished and eliminated by raising the minimum amplitude and number of cycles to 20. This procedure is being enhanced for screening antitremor agents and for elucidating the possible mechanism for Parkinsonism.