Effects of Some Antiparkinsonism Drugs and centrally Acting Muscle Relaxants on the Intercollicular Decerebrate Rigidity in Rats

The decerebrate rigidity in rats was prepared by means of transection between the inferior and superior colliculi. The strength of the rigidity was measured as electromyographic (EMG) activity of the rigid gastrocnemius muscle. Because of some similarity between Parkinsonism and intercollicular decerebrate rigidity, the effects of several antiparkinsonism drugs as well as centrally acting muscle relaxants on this type of the rigidity were studied. A small dose of chlorpromazine (125 μg/kg, i.v.) markedly reduced the rigidity. The inhibitory effect of trihexyphenidyl, biperiden, orphenadrine and tigloidine injected intravenously was dose-related. L-Dopa exerted only a little effect on the EMG activity of the rigid muscle. Mephenesin, methocarbamol, tolperisone, phenprobamate and diazepam were all effective in reducing the rigidity. These results are discussed in relation to data on their effects upon the crossed extensor reflexes in spinal chicks.