A method for measuring drug-induced changes in limb muscle tone in the rat

A method for measuring the time-course and magnitude of changes in rat hind leg muscle tone in vivo is described in detail. The rat is held in a restraining box and the apparatus pushes each hindpaw from behind a distance of 1 cm and measures the force required to briefly hold each leg in the displaced position. The push-relax cycle is repeated every 45 s. Identical measurements were obtained from the 2 hind legs. Experimental results are presented to demonstrate the potential of the technique for investigating the effects of drugs on muscle tone. Morphine, which is known to cause rigidity, increased the force required to displace the hind legs. Muscle tone was reduced in rats that were lightly anaesthetized.