Quantitative grip strength assessment as a means of evaluating muscle relaxation in mice

The effects of various centrally acting drugs and some peripherally acting agents on the forelimb grip strength of CD-1 mice were explored. Forelimb grip strength was assessed by use of a strain gauge to measure the lateral pull force, in grams, exerted by mice as an index of muscle relaxation. The muscle relaxants, diazepam, midazolam, baclofen, methocarbamol, dantrolene sodium and the neuromuscular blocking agents, succinylcholine and pancuronium bromide, dose-dependently reduced forelimb grip strength. 2-Amino-7-phosphonoheptanoic acid (AP7), which has also been shown to have muscle relaxant effects, also reduced grip strength. Pentobarbital, ethanol, phencyclidine, ketamine and chlorpromazine reduced grip strength at doses which produced behavioral impairments. Lithium chloride, a toxic compound used to induce taste aversions, and clonidine, at doses which affect blood pressure, body temperature and locomotor activity, did not affect grip strength. In addition, stimulant doses of amphetamine and caffeine, but not of morphine, increased grip strength in a dose-dependent manner. These results extend previous findings and suggest that this forelimb grip strength procedure may be a useful screening test for the identification of the potential muscle relaxant properties of drugs.