Swallow pattern generation includes a parasympathetically mediated heart rate change and a sympathetically mediated pressure change in a modified artificially perfused rat preparation

Swallowing is a primitive but complex behavior that must coordinate with respiration and the autonomic nervous system in order to maintain homeostasis. However, the participation of sympathetic and parasympathetic drive during swallow behavior have not been well-studied. To determine the effects of swallow on autonomic outflow, we stimulated swallow with oral water infusion in a modified non-paralyzed working heart-brainstem preparation of rats (P23-P28). Rather than transecting the animal, the spinal cord was left intact. We recorded electromyograms from the diaphragm and laryngeal and submental muscle complexes, as well as heart rate (HR) and perfusion pressure (PP). We hypothesized that we would observe a transient increase in PP during swallow that would be mediated by sympathetic α-adrenergic receptors. We expected HR to either remain unchanged or increase during swallow, and any changes in HR to be parasympathetically mediated. PP increased transiently during swallow, as predicted. However, swallows produced by the in situ preparation were surprisingly accompanied by a decrease rather than an increase in HR. To confirm that these changes were due to autonomic activity, we applied the autonomic ganglionic blocker hexamethonium bromide, which decreased baseline PP and HR and indeed eliminated the changes in PP and HR during swallow. To elucidate the mechanism by which these autonomic changes during swallow occurred, we administered several different drugs targeting autonomic receptors. The β-adrenergic antagonist atenolol increased baseline PP and decrease in HR as expected. Swallows still occurred under atenolol with no change in the PP response during swallow, nor were there any changes in the time to reach the peak PP. The α1 receptor antagonist prazosin decreased baseline PP as expected without any effect on HR. Prazosin unexpectedly failed to change the PP response to swallow, but decreased the time to reach peak PP. We performed bilateral vagotomy caudal to the recurrent laryngeal nerve to remove parasympathetic outflow to the heart. As expected, this eliminated respiratory sinus arrythmia and increased baseline HR. The HR change during swallow was also eliminated, but there were no significant changes to baseline PP nor the PP response during swallow. Finally, we administered scopolamine, a M2 muscarinic acetylcholine receptor antagonist. Scopolamine did not change baseline parameters. As expected, scopolamine did not change PP during swallow. Similar to the bilateral vagotomy, no drop in HR occurred during swallow after scopolamine administration. We speculate that, in this preparation, the decrease in HR is a baroreflex response to the increased PP produced with swallow. We further speculate that the PP swallow response was retained under prazosin due to residual rapid, transient sympathetic vasoconstrictive activity mediated by ATP and/or neuropeptide Y co-released with noradrenaline. Our results demonstrate that swallow is coupled with autonomic changes mediated by several receptors, including an excitatory vasomotor sympathetic pathway to control upper airway motor activity. However, the reduced in situ preparation does not produce all the known changes in more intact preparations. Funded by NIH Grants: NS110169, HD110951, and the Ora B., Charles N., and Beatrice L. Davisson Faculty Scholar in the Department of Speech, Language & Hearing Sciences This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.