Electrophysiological comparison between catechol- and urea-induced myoclonus models in the rat

Catechol- and urea-induced myoclonus models in the rat were electrophysiologically compared to clarify pathophysiological differences. Catechol-induced myoclonus had various similarities with cortical reflex myoclonus in that there were electroencephalogram (EEG) discharges prior to myoclonic discharges, a spread of myoclonic discharges from the rostral to the caudal site, and a high amplitude somatosensory evoked potential (SEP). In urea-induced myoclonus, there were no EEG discharges related to myoclonic discharges and no enlarged SEP components as in reticular reflex myoclonus. Catechol-induced myoclonus had two evoked EMG responses of the biceps femoris at mean onsets of 8.0(C1) and 13.4 (C2) ms, and urea-induced myoclonus had a response (U1) at the mean onset of 10.2 ms. A study of the effects of various lesions in the central nervous system on these evoked EMG responses suggests that C1 is a monosynaptic spinal reflex. C2 which disappeared when the bilateral sensorimotor cortex for the hind limb had been resected and the lesion cooled is generated by the deep cerebral structures, such as the thalamus or basal ganglia, and U1 originates in the brain stem reticular formation. These results imply definitive differences of the pathophysiological mechanisms between catechol- and urea-induced myoclonus.