Vagal control of thermal panting in mammals and birds.

1. The role of the vagus nerves during normal respiration and thermal polypnoea was examined in four species of mammals and four species of birds by lung/air sac inflation and cervical vagotomy.2. The Hering-Breuer inflation reflex could be elicited in all of the mammals during both normal respiration and panting; it was present in the fowl and pigeon at normal body temperature only.3. Section of one vagus during hyperthermia reduced respiratory frequency in most animals and increased depth. Bilateral vagotomy had little further effect in the panting rabbit, lamb and pigeon, but abolished rapid respiration in the rat, guinea-pig, fowl, duck and quail.4. Vagotomized lambs and pigeons started panting in response to increasing body temperature, although the rate attained was slower than in intact animals. Guinea-pig, rat, fowl and quail did not pant under these conditions.5. Appropriate afferent vagal stimulation in the vagotomized fowl maintained normal respiration or thermal panting.6. It is concluded that panting can, in some mammals and birds, be controlled by central mechanisms alone, while in others it depends on extrinsic stimuli mediated by way of the vagus nerves.