The effect of α-methyl-p-tyrosine and substantia nigra lesions on spinal motor activity in the rat

The effects of α-methyl-p-tyrosine (αMT) and of bilateral lesioning the substantia nigra on spinal motor activity were studied in rats and compared with reserpine rigidity. αMT, as well as the lesions produced by electrocoagulation or microinjection of 6-hydroxydopamine (6-OH-DA) produced rigidity signalled by tonic activity in the electromyogram during sustained muscle stretch, high α- and low γ-reflex activity, and a short latency of α-reflex discharges. The effect on spinal motor activity of αMT and of bilateral electrocoagulation of the substantia nigra was antagonized by DOPA. Motor disturbances following microinjection of 6-OH-DA into both substantiae nigrae were not influenced by DOPA, metamphetamine or amantadine. Atropine abolished the effect of substantia nigra lesioning by electrocoagulation or by microinjection of 6-OH-DA. On the basis of the results it is concluded that the rigidity produced by reserpine is due to dopamine depletion in the striatum.