Developmental changes in the hypoxic ventilatory response in C57BL/6 mice

C57BL/6 mice are the strain into which most null mutations for neurotransmi tters or their receptors are backcrossed. A number of these transgenic mice have recently been shown to have an abnormal respiratory phenotypes howeve r, the postnatal development of the ventilatory response to hypoxia has not been characterized in C57BL/6 mice. The effect of 8%, oxygen for 5 min was examined in mice at five periods from P1 to P30 using a body plyethysmogra ph. Neonatal and juvenile animals from P7 to P30 showed a biphasic pattern in hypoxia in which the increase in minute ventilation achieved in the firs t min declined towards baseline by the fifth minute and was decreased below baseline in the first minute of return to air breathing. In contrast P1-P3 C57BL/6 mice had a sustained increase in both respiratory frequency and ti dal volume and their minute volume remained above baseline on return to air . The decline in oxygen consumption., measured in the fifth minute of hypox ia, was not different in P1-P3 mice compared to P8-P10. These results sugge st that the earliest response to hypoxia of the respiratory system in this strain is not characterized by a time dependent depression as seen in older animals and in species whose motor systems are relatively more developed a t birth. (C) 2001 Elsevier Science B.V. All rights reserved.