MODIFICATION OF CORTICALLY EVOKED RHYTHMIC CHEWING AND SWALLOWING FROM MIDBRAIN AND PONS

抄録

In rabbits under light ether anesthesia, the midbrain and upper pons were explored with tetanic stimuli to alter cortically evoked rhythmic chewing and swallowing. The effects of various surgical sections of the brain stem upon these phenomena were also studied.
1. Stimulation in an extensive midbrain area produced a diminution of rhythmic chewing, and very often a complete arrest in the jaw-opened position, whereas that at two discretely localized areas produced an enhancement. Bilateral masseteric EMGs revealed a response comparable to the above, i. e., the activity decreased symmetrically during diminution, and accelerated during enhancement of rhythmic chewing. During the stimulation, elicitation of swallowing was consistently diminished without regard to changes occurring in rhythmic chewing.
2. Stimulation at the upper pons produced an arrest of rhythmic chewing, with the jaw closed. At the same time the masseteric EMG was tetanically activated ipsilaterally, while being quiescent contralaterally. Another area delimited within or near the preceding one was responsible for a conspicuously long-lasting bout of repetitive swallowing.
3. Longitudinal midline splits extending from the corpus callosum to the rostral border of the superior colliculi had no effect upon cortically evoked rhythmic chewing and swallowing or upon changes in those induced by brain stem stimulation. A short longitudinal cut at the superior colliculi largely eliminated the effect of enhancement, leaving that of diminution or arrest of cortically evoked rhythmic chewing. A similar split involving the lower midbrain and upper pons completely abolished cortically evoked rhythmic chewing. None of these midline splits, however, abolished swallowing, although it was reduced.
4. Transverse hemisection just rostral to the superior colliculus eliminated cortically evoked responses ipsilaterally, leaving them intact contralaterally, whereas midpontine hemisections did not alter the responses.
5. After complete decerebration at the supracollicular level the cortically evoked response was abolished but the irregular chewing and swallowing persisted with brain stemst imulation. Mid-pontine transection abolished such brain stem-elicited chewing and swallowing, leaving reflex swallowing intact.
6. On the basis of these findings the neural control of rhythmic chewing and swallowing is discussed in relation to the reticular activating and inhibiting systems, and its probable arrangement is tentatively proposed.