[Dependence of electromyographic reaction indices of the muscles-antagonists and stiffness of the elbow joint on its extension velocity before and after the injection of neurotoxin].

Electromyographic (EMG) activity of the elbow joint muscles elicited by passive extension were recorded in anaesthetized cats before and after MPTP injection (7-10 mg/kg intramuscularly). It was shown that after injection of such dose of MPTP amplitude and duration of the stretch-related M2-3 --components of EMG increased and recovered on 9-10 day after the chemical injection. Perturbation of an external extensor loading applied to the forearm with different velocities elicited m. biceps brachii EMG reactions which amplitude in norm correlated with a muscle stretch velocity and duration correlated with applied force duration. The MPTP injection led to reversible changes of these stretch-reflex parameters. In norm elbow joint stiffness showed a linear dependence on external loading velocity. The MPTP injection resulted in joint stiffness decrease during the quick perturbation of loading. The stiffness recovery was a longer process comparing to the EMG recovery. It is concluded that the evoked stretch reflex parameter changes as a result of artificially produced dopamine deficiency are insufficient for the total stiffness increase and rigidity manifestation and that amplitude and duration increase of stretch responses may come earlier than parkinsonian rigidity manifestation. It is supposed the decisive importance of supraspinal influences on rigidity development in dopamine function deficiency conditions.