Abstract
Active contraction of the diaphragm and other inspiratory pump muscles during swallow create a negative thoracic pressure to improve the movement of the bolus (food/liquid) into the esophagus. We tested the hypothesis that dorsomedial medullary inspiratory neurons, including the nucleus tractus solitarius (NTS, pre-motor to the phrenic) would be active during swallow induced by oral water infusion. We recorded neurons in the NTS and medial reticular formation in anesthetized spontaneously breathing cats, and induced swallow by injection of water into the oropharynx. Our results indicate that: 1) a majority of inspiratory cells in the dorsomedial medulla are active during swallow, 2) expiratory neurons are present in the medial reticular formation (deeper to the NTS) in unparalyzed cats and a majority of these cells decreased firing frequency during swallow. Our findings suggest that the dorsomedial medulla is a source of inspiratory motor drive during swallow and that a novel population of breathing-modulated neurons that also are modulated during swallowing exist in the medial reticular formation in unparalyzed animals.
Highlights
The “swallow-breath” was of great interest in the earliest experiments in deglutition [1, 2]
Eighteen neurons were recorded within the region of the nucleus of the tractus solitarius (NTS) (
Within the NTS 94% (17/18) were inspiratory (2 were phase spanning), 89% (16/18) were active during swallow, and 39% (7/18) increased in firing frequency (FF) over that observed during breathing (Tables 2 and 3)
Summary
The “swallow-breath” (i.e. schluckatmung in German) was of great interest in the earliest experiments in deglutition [1, 2]. While there have been relatively few studies recently, Bosma [2] stated that the schluckatmung “has been studied extensively”, and references the work of several groups of European scientists. This issue was discussed by Marckwald [1] in Appendix I, with the ultimate conclusion that diaphragm movement is an active portion of swallowing produced by the swallow central pattern generator (CPG). Summarizing earlier work together with his studies in the rabbit he drew the following conclusions: a) the phrenic motor burst is approximately 200–300 ms after the burst of the mylohyoid; b) ablation of the phrenic nerve did not suppress all movement of the thorax during swallowing; c) central apnea
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