The expiration reflex during ontogenesis in the rat.

The authors studied the elicitability of the expiration and aspiration reflex and of the respiratory reaction from the tracheobronchial area in 131 anaesthetized rats (aged 1-15 days, adult and biologically old). They found that the expiration reflex could be elicited, in the rat, from the first day of life, at a time when other respiratory reflexes were not yet stable. In young rats, the expiration reflex was often followed by a cough reaction which was absent in adult animals. The findings indicate that the expiration reflex is one of the most important respiratory reflexes of the early postnatal period in the rat, because the aspiration reflex and the respiratory reaction from the bronchi were not stable until the 15th day of life. In biological old rats, the expiration reflex is less frequently elicited and its intensity attains about half the value found in adult animals. The aspiration reflex and the respiratory reaction from the bronchi are likewise less readily elicited than in adult animals, but when the intensity of their maximum expiratory effort is increased, it is far greater.