Abstract
Rationale: Cough is rarely reported during neonatal period in healthy newborns but it is the most frequent respiratory symptom in the first months of life. Consistently, studies on the maturing newborns of different animal species have shown that cough reflex (CR) from larynx is absent at birth and develops over a span of 2-3 weeks, whereas expiration reflex (ER) is already present at birth. This suggests that CR and ER may undergo a maturational process during childhood.
Objective: To study the incidence, stimulus threshold and type of defensive response from tracheobronchial region to mechanical stimulation in young rabbits at different ages.
Methods: Forty three rabbits (7 days n=8, 15 days n=5, 30 days n=17, 90 days n=13) underwent a discrete mechanical challenge of trachea (50 – 2400 ms) during pentobarbital anesthesia.
Results: Both CR and ER were present by 7 days post natal age. However, the incidence of expiration reflex was significantly higher at 15th day (72%) compared to 30th day (18%) and 90th day (42%) (p< 0.01), whereas the incidence of CR containing responses was significantly lower at 15th day (28%) than at 30th (82%) and 90th day(76%) (p< 0.01).
Conclusion: Our results have shown differences in CR and ER incidence during aging pointing to the maturational process of respiratory defensive responses. In younger animals, most responses are ER and the incidence of CR is low. Based on the assumption that the afferent pathway is similar for ER and CR, the current findings support neuronal plasticity of brainstem cough centre as a mechanism of CR maturation during early development.
- © 2014 ERS