[Effect of polysynaptic flexion reflex on monosynaptic reflexes of calf muscles prior to and following intramuscular injection of ethylbenzatropine in drug-induced muscle rigidity].

In patients with drug-induced parkinsonism and in healthy subjects the effect of stimulation of low-threshold skin fibres of sural nerve producing the polysynaptic flexion reflex of the short head of the biceps femoris muscle on the monosynaptic H reflex of calf muscles was studied before and after administration of ethylbenzatropine. In healthy subjects stimulation of low-threshold skin nerve was followed by facilitation of H reflex in the time of 70 to 200 msec. from the conditioning stimulation to the test stimulation. After one single intramuscular dose of ethylbenzatropine this late facilitating effect disappeared. In patients with drug-induced parkinsonism stimulation of afferent fibres of flexion reflex failed to cause late facilitation of H reflex and one dose of ethylbenzatropine brought no changes. During systematic administration of the drug an evident tendency for facilitation of H reflex was observed, similarly as in healthy subjects. The results obtained in healthy subjects and in patients with drug-induced parkinsonism are explained as evidence of inhibitory action of noradrenaline in certain chains of spinal interneurons, since noradrenaline release in the spinal cord is determined by the striatal equilibrium between the cholinergic and dopaminergic systems. The corrective action of ethylbenzatropine would depend on its central action on certain spinal chains of interneurons determining transmission of impulses from dermal afferent nerves to alpha motoneurons.