Quantitative analysis of drug-induced tremor in mice

A method of analyzing tremor in mice was developed using a power spectral analysis of the random current induced by the movement of a magnet attached to a mouse, on a wire coil. The power spectral density function defined the frequency composition of the tremor, and the mean square value of the data in any frequency range of concern was determined. It was possible to determine qualitative differences in the tremor caused by various tremorgenic agents, and to differentiate the drug-induced tremor from spontaneous motor activity. The power spectral densities of the tremorine- and oxotremorine-induced tremors were tentatively expressed as the sum of 3 main components (Cauchy distribution) with different peak frequencies, consisting of the spontaneous motor activity component and two tremor components. On the other hand, the power spectral densities of the harmaline-induced tremor were expressed as the sum of two components with two peak frequencies, and the plots of the power spectral densities versus frequency, consisting of the spontaneous motor activity component and a tremor component. The frequency of the peak spectral density was almost independent of the dose of tremorgenic agents, but changed slightly with the lapse of time after their injection. The severity of the tremor was determined quantitatively in terms of the sum of the mean square value. The sum of the mean square value for a period of 45 min after the injection of tremorine, changed in a dose-dependent manner. The severity of the tremor was different for each of the mouse strains. The method studied in the present paper is expected to be utilized for the quantitative examination of the fine motor movement of the experimental animal, particularly, for the screening test of new anti-tremor drugs.