Effects of decortication and carotid sinus nerve section on ventilation of the rat

The effect on ventilation of exposure to hypoxic, hypercapnic and hypoxic/hypercapnic gas mixtures was studied before and after functional decortication of intact rats and rats in which the carotid chemoreceptors had been disconnected. Unanaesthetized rats responded to both hypoxia and hypercapnia with an increase in minute ventilation (V) through increases in both frequency (f) and tidal volume (VT). Decortication led to a greater V response to CO2. This was through an effect on f, rather than VT. Carotid sinus nerve section (CSNS) caused a lessening in the V response to gas mixtures, f and VT being equally affected. Decortication, following CSNS, increased the V response but this time through increased VT rather than f. This effect on VT was not specific to any particular gas mixture. It is concluded that the carotid body chemoreceptors, together with the bulbopontine rate controller, influence the response to CO2. It is further suggested that this integration takes place in the reticular formation and is normally under some degree of inhibition from the cerebral cortex.