Harmaline-induced rhythmic activities of bulbar reticular cells and antagonistic muscles in the rat: a simultaneous...

The harmaline-induced tremor of antagonistic muscles is studied in the anaesthetized rat. By recording simultaneously both the rhythmic EMG-activities in flexor and extensor muscles and the concomitant tremorogenic bulbar reticular discharges, we discovered two facts. 1) The extensor burst precedes the flexor muscle discharge by about 10 msec, contrarily to the close synchrony expected from anterior descriptions of harmaline tremor. 2) The previously observed periodical modulation of olivary and Purkinje cell rhythmic activities is transferred, through the reticular formation to the spinal level, in the form of an alteration of periods with tremor and periods with tonic coactivation of antagonistic muscles. The implication of the myotatic loop in the second fact is discussed.