INACTIVATION OF THE PONS BLOCKS MEDULLARY-INDUCED MUSCLE TONE SUPPRESSION IN THE DECEREBRATE CAT

The pontomedullary region is responsible for the reduction of muscle a ctivity in rapid-eye-movement sleep and contributes to the control of muscle tone in waking. This study sought to clarify the nature of the interaction between the pontine and medullary reticular formation in m ediating muscle tone suppression. The degree of medullary-induced neck muscle tone suppression in the decerebrate cat was assessed before an d after microinjection of lidocaine into the pontine reticular formati on. Medullary stimulation-induced suppression of neck muscle tone was blocked after pontine lidocaine microinjection. The maximum blockade w as observed at 16.6 minutes on average after the injection, and recove ry occurred within 45 minutes. We conclude that descending mechanisms from the medulla are not sufficient for the triggering of muscle tone suppression. A two-way interaction between the medulla and pens is hyp othesized to play a crucial role in the control of muscle tone.