Effect of the prenatal maternal environment on the control of breathing during non-rapid-eye-movement sleep in the developing lamb
Symonds ME., Lomax LA., Kenward MG., Andrews DC., Johnson P.
This study examines the effects of altering the prenatal maternal metabolic and hormonal environment via chronic cold exposure of under-fed ewes on developmental changes in breathing control of developing lambs. Breathing frequency and timing were measured during non rapid-eye-movement (non-REM) sleep in lambs born from either shorn or unshorn ewes after being maintained for at least one hour at warm (28-19°C) and cool (14-5°C) ambient temperatures at 1, 4, 14 and 30 days of age. Breathing frequency and oxygen consumption were significantly higher in 1 day old lambs born from shorn ewes compared with those lambs born from unshorn ewes, at both warm and cool ambient temperatures. In the shorn group breathing frequency decreased between 1 and 4 days of age and continued decreasing up to 30 days of age, during which period inspiratory and to a greater extent expiratory time, lengthened. Laryngeal 'braking' of expiratory airflow was observed in more than 50% of lambs born from shorn ewes during non-REM sleep in the warm at 4, 14 and 30 days of age, and in the cold at 14 and 30 days of age. In contrast, lambs born from unshorn ewes showed no change in breathing frequency between 1 and 4 days of age, but a decrease was observed between 4 and 14 days of age, whilst laryngeal 'braking' of expiratory airflow was rarely observed at any age. It is concluded that the development of breathing control over the first month of postnatal life can be affected by alterations in the fetal environment elicited by chronic cold exposure of the mother.