PONTINE-INDUCED GENERALIZED SUPPRESSION OF POSTURAL MUSCLE TONE IN A REFLEXIVELY STANDING ACUTE DECEREBRATE CAT

In a reflexively standing acute decerebrate cat, the pontine tegmentum was electrically stimulated and the effects on postural muscle tone a nd locomotor movements evoked by stimulation of the mesencephalic loco motor region (MLR) were studied. A stimulating microelectrode was plac ed systematically at 1-mm increments throughout the pons (H - 2 to H - 10) at levels ranging from P0.0 to P6.5 dorsoventrally and mediolater ally from LR0 to L4 or R4. Another stimulating microelectrode was plac ed in the physiologically identified MLR. Stimuli delivered to the dor somedial regions of the pontine tegmentum (P3 to P4, LR1.5 to 2.5, H - 4 to H - 6) resulted in simultaneous and bilateral suppression of ton ic activities in the neck, lumbar back, forelimb and hindlimb muscles. The pontine inhibitory sites corresponded to the medial area of the c entral tegmental field (FTC) and the central area of the gigantocellul ar tegmental field (FTG), bilaterally. Effects of pontine induced supp ression on those muscles were stimulus frequency and stimulus intensit y-dependent and the effects persisted even after termination of the st imulation. With concomitant pontine stimulation, MLR-evoked locomotor movements were suppressed along with prolongation of the forelimb and hindlimb step cycles.