Quantification of tremor in rats induced by physostigmine

A simple and accurate device for recording tremor intensity in unanaesthetized and unrestrained rats is described. The physical measures of tremor are shown to have several advantages over previous devices. First, the new apparatus, unlike some earlier ones, does not restrict the animal's movements to an unusually small cage, with weighty mechanical devices or with electrical leads. Second, most earlier methods for measuring tremor use a subjective rating scale. However, the present method uses objective and reliable measures. In a double-blind, illustrative experiment involving complete crossover, Wistar rats were randomly injected IP with physostigmine in doses of 0.2, 0.4, 0.6 and 0.8 mg/kg or the corresponding amount of 0.9% NaCl solution as control. The recorded tremor intensity showed a clear dose-response relationship for physostigmine. Moreover, linear regression of the dose-response relationship showed that tremor intensity increased linearly with increasing doses of physostigmine. The cholinergic antagonist atropine (0.3 mg/kg SC) antagonized physostigmine-induced tremor, whereas methylatropine (0.3 mg/kg SC) tended to potentiate it. These results show that the technique described is suitable for quantification of tremor intensity in rats and for testing drug interactions on physostigmine-induced tremor.