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A procedure for quantifying whole-body tremors in mice was developed. Displacement of a free-floating platform by animal movement created a change in resistance across a strain gauge. The resulting resistive changes were assessed as voltage fluctuations by a wheatstone bridge and converted into an intensity-frequency profile by a series of calculations involving Fourier transformations. Movement profiles of normal mice were characterized by high-intensity, low-frequency peaks. Administration of oxotremorine, 2.5 mg/kg, ip, produced numerous high-frequency, high-intensity peaks within 5 min of administration. The peak frequency at 5 min after oxotremorine was approximately 15 Hz, and within 30 min the intensity-frequency profile had returned to control levels. In dose-response studies, a slight decrease in exploratory activity and initiation of low-level tremors was observed after 0.5 mg/kg. The most severe tremors were detected after a dose of 1.0 mg/kg. The peak frequency remained at approximately 15 Hz at 1.0 to 5.0 mg/kg, but varied greatly in intensity. This study describes an inexpensive, quantitative, sensitive, and rapid technique for quantifying tremors in mice.

The effect of cyanide on whole-brain calcium levels was determined in mice administered KCN and correlated with the neurotoxic signs manifested during acute cyanide poisoning. KCN (10mg/kg, sc) significantly increased whole-brain total calcium levels from 48.1 +/- 1.8 to 66.5 +/- 3.9 micrograms/g dry wt within 15 min after administration. The levels remained elevated for 3 hr and returned to control readings after 12 hr. Dose-response studies revealed KCN, at doses of 10-15 mg/kg, produced significant elevations of whole-brain calcium 30 min after administration. No measurable effect was obtained from lower doses which suggested a threshold effect. Pretreatment 15 min before KCN with diltiazem, a calcium channel blocker, prevented the cyanide-induced rise in whole-brain total calcium. Cyanide-induced tremors, which are centrally mediated symptoms of intoxication, were quantified and correlated with the observed changes in whole-brain calcium. Tremors were detected at 10 and 12 mg/kg KCN and peak intensity was observed at 15 min postcyanide. Pretreatment with diltiazem markedly attenuated the cyanide-induced tremors. It appears that a correlation exists between cyanide-induced change in whole-brain calcium and tremors. This study suggests that intraneuronal calcium may play an important role in mediating cyanide neurotoxicity and calcium channel blocking agents may be useful in limiting the severity of the centrally mediated symptoms of acute cyanide intoxication.