Effects of superior layngeal nerve section on ventilation in neonatal guinea-pigs

Ventilation was measured by barometric plethysmography in conscious, 10-14 day-old guinea-pigs with superior laryngeal nerves (SLN) intact or sectioned. In SLN-intact animals, hypercapnia caused concentration-dependent increases in respiratory frequency, tidal volume and minute ventilation but hypoxia had no effects. SLN section reduced respiratory frequency and minute ventilation during normoxia and reduced the ventilatory response to 6% CO₂. In the same animals under anaesthesia, upper airway (UA) cooling decreased respiratory frequency and increased peak inspiratory flow in SLN-intact but not in SLN-sectioned animals. CO₂ in the UA caused a tachypnoea which was also present in SLN-sectioned animals and when the nose was bypassed. These results show that UA afferents participate in ventilatory control in neonatal guinea-pigs. Moderate UA cooling causes a SLN-dependent decrease in respiratory frequency but UA CO₂ causes tachypnoea which is not SLN-mediated and contrasts with the inhibitory effect of UA CO₂ on breathing described in adults of other species.