[Effect of trihexphenidyl on the excitability of alpha motor neurons of the foot plantar flexor in chemically induced parkinsoniam rigidity].

For assessment of the effect of trihexiphenidil on the excitability state of the alpha-motoneurons of the plantar flexor of the foot in patients with drug-induced parkinsonian rigidity curves of the excitability of motoneurons of the soleus muscle were plotted in two variants of experiments: I. with afferent stimulation of the Ia fibres of the soleus muscle as the conditioning and testing stimulus (tibial nerve in the popliteal fossa), II. with afferent stimulation of Ia fibres of the anterior tibial muscle (peroneal nerve behind the fibular capitulum) used as the conditioning stimulus and stimulation of the tibial nerve as the testing stimulus. These investigations were carried out on 12 psychiatric patients who received no drugs at the time of these investigations (control group), 13 similar patients treated with chlorpromazine, 12 treated with phenothiazine compounds with piperazine ring in the side chain. The investigations were repeated 30-50 min. after oral administration of trihexiphenidil 5 mg. In variant I typical excitability curves were obtained and 5 phases could be discerned in them. In patients treated with piperazine-containing phenothiazine derivatives inducting more significant parkinsonian effects phase III - depression - was significantly shortened, and the excitability was raised in phase IV. In variant II phases III and IV were reversed and in phase IV a rise in excitability was observed in place of depression. In variant II in the group of drug-induced parkinsonism as compared with controls the rise in exictability was greater in phase III and depression in phase IV was smaller. The effect of trihexiphenidil in variant I depended on the initial state. In controls and in patients treated with chlorpromazine trihexiphenidil reduced the duration of phase III of depression and decreased its intensity. In atients treated with phenothiazines containing the piperazine ring depression in phase III was weak but increased after trihexiphenidil administration and increased excitability in phase IV was decreased. The curves became similar to those obtained in controls. In variant II in the control group excitability in phase III increased after trihexiphenidil administration.