Implication of the vagus nerve in breathing pattern during sequential swallowing in rats

The ventilatory pattern during sequential swallowing is influenced by the vagal activity. As the vagus nerve is paired and mixed, we aimed (1) to determine if vagal implication in swallowing and breathing coordination is symmetric. (2) to study the importance of vagal afferences in swallowing and breathing coordination. Sixty two Wistar rats (7-11weeks, 260-400g) were studied by barometric plethysmography. In the first part of the study, we determined the effects of a right cervical vagotomy and the effects of a left cervical vagotomy on ventilatory pattern at rest and during sequential swallowing (14 rats with right vagotomy, 14 rats with left vagotomy and 14 rats with sham surgery). Comparisons of ventilatory variables were made between right and left vagotomized animals. Thereafter, we determined the effects of electrical vagus nerve stimulation (VNS) on ventilatory pattern at rest and during sequential swallowing (10 rats with electrical VNS and 10 rats with sham VNS). We showed that a right or a left cervical vagotomy does not alter ventilation at rest, but induces during sequential swallowing a decrease in respiratory rate (RR) (p<0.001) and mean inspiratory flow (VT/TI) (p<0.01) compared to baseline. These modifications were not observed following sham surgery and there were no differences in ventilatory variables at rest and during sequential swallowing between right vagotomized rats and left vagotomized rats (p>0.05). Electrical VNS had no effect on ventilation at rest, but it minimized during sequential swallowing a decrease in RR related to a local alteration of the vagus nerve after placement of the electrodes as shown following sham VNS. In conclusion, the implication of vagus nerve in breathing pattern during sequential swallowing seems symmetric and influenced by activation of the vagal afferent pathway. These data can be useful when testing electrical VNS in swallowing disorders.