Role of the pontine reticular formation in the neural organization of deglutition.

Abstract

Under light ether anesthesia, the pons was explored with tetanic stimuli to produce or modify rhythmic swallowing in rabbits. The effects of various surgical and pharmacological procedures upon the responses and the topography of the brain stem area concerned were studied.1) Stimulation of the appropriate area in the pons yielded prolonged repetitive swallowing. The number of swallows that occurred during stimulation was maximum at a certain stimulus intensity (ca. 5 volts) and declined with use of greater intensity. During stimulation above 8 volts no swallowing could be seen. However, the number of swallows occurring after cessation of stimulation was increased by higher stimulus intensities.2) The pontine area concerned was delimited bilaterally in the reticular formation dorsolateral to the superior olivary nucleus and ventral to the motor trigeminal nucleus.3) Simultaneous stimulation of the anterolateral frontal cortex greatly enhanced the repetition of swallowing occurring from pontine stimulation.4) The swallowing response diminished markedly after supracollicular decerebration or restricted bilateral ablation of the frontal cortical area. It was also reversibly suppressed by topical surface application of GABA or Xylocaine or local cooling of the frontal cortex.5) Pontine stimulation also produced rhythmic chewing and salivation as well as swallowing. However, cortical influences on chewing were greater than on swallowing.6) Slight facilitation (when pontine stimulation did not exceed 5 volts) and powerful inhibition (at higher intensities) were effected for swallowing elicited by either stimulation of the superior laryngeal nerve or water in the oropharynx.7) Destruction of the relevant pontine area by electrocoagulation or separation by surgical transection at the ponto-medullary border caused no essential alteration of the elicitation or performance of reflex swallowing.8) On the basis of these findings and those previously obtained, an intricate neural arrangement connecting cerebral cortex, brain stem reticular formation, medullary integrative center, and afferents from oropharynx for the control of swallowing is schematized and its mode of operation is discussed.