HALOPERIDOL-INCREASED MUSCLE TONE IN RATS AS A MODEL OF PARKINSONIAN RIGIDITY

The aim of the present study was to find out whether haloperidol-induc ed rigidity was similar to that seen in parkinsonism. Simultaneous mea surements of the muscle resistance (mechanomyogram, MMG) of the hind f oot to passive flexion and extension in the ankle joint, as well as de termination of the electromyographic (EMG) activity of the gastrocnemi us and tibialis anterior muscles of rats were carried out. Haloperidol was injected in doses of 0.5-10 mg/kg 1 h before the start of measure ments. Haloperidol increased, in a dose-dependent manner, the muscle r esistance of the rat's hind leg to passive movements. Muscle rigidity was accompanied with an increase resting, as well as in the stretch-in duced long-latency EMG activity (in which supraspinal reflexes are mos t probably involved) in both those muscles, whereas the short-latency EMG activity (first large bursts of EMG activity, beginning ca. 9 ms a fter the start of a movement, probably of a spinal origin) was signifi cantly decreased. The obtained results suggest that the haloperidol-in creased MMG/EMG activity might be a good model of parkinsonian rigidit y.