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 and locomotor movements evoked by stimulation of the mesencephalic locomotor region (MLR) were studied. A stimulating microelectrode was placed systematically at 1-mm increments throughout the pons (H - 2 to H - 10) at levels ranging from P0.0 to P6.5 dorsoventrally and mediolaterally from LR0 to L4 or R4. Another stimulating microelectrode was placed in the physiologically identified MLR. Stimuli delivered to the dorsomedial 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 tonic activities in the neck, lumbar back, forelimb and hindlimb muscles. The pontine inhibitory sites corresponded to the medial area of the central tegmental field (FTC) and the central area of the gigantocellular tegmental field (FTG), bilaterally. Effects of pontine induced suppression on those muscles were stimulus frequency and stimulus intensity-dependent and the effects persisted even after termination of the stimulation. With concomitant pontine stimulation, MLR-evoked locomotor movements were suppressed along with prolongation of the forelimb and hindlimb step cycles.