Developmental hyperoxia attenuates the hypoxic ventilatory response in Japanese quail (Coturnix japonica)

Abstract

Early life experiences can influence development of the respiratory control system. We hypothesized that chronic hyperoxia (60% O(2)) during development would attenuate the hypoxic ventilatory response (HVR) of Japanese quail (Coturnix japonica), similar to the effects of developmental hyperoxia in mammals. Quail were exposed to hyperoxia during prenatal development, during postnatal development, or during both prenatal and postnatal development (for approximately 2 or 4 weeks). HVR (11% O(2)) was subsequently assessed in adults (>6 weeks old) via barometric plethysmography and compared to quail raised in normoxia (i.e., control). The HVR of quail exposed to hyperoxia both prenatally and postnatally was reduced 50-60% compared to control quail whereas postnatally exposed quail exhibited normal HVR. The effects of prenatal hyperoxia on HVR were equivocal and depended on how HVR was expressed. We conclude that developmental exposure to 60% O(2) attenuates the HVR in quail and that the critical period for this plasticity encompasses the late prenatal and early postnatal periods.

Fig. 1

Rearing protocols used in this experiment. Hatching normally occurs after 16–17 days of incubation in Japanese quail (dotted line). In this diagram, open bars represent time periods during which quail were exposed to normoxia (21% O₂) whereas shaded bars represent time periods during which quail were exposed to hyperoxia (60% O₂). Thus, quail in the NN group were exposed to normoxia throughout development and quail in the HH-4wk group were exposed to hyperoxia for a little more than 4 weeks (31 days) spanning both prenatal and postnatal development. The remaining groups were exposed to hyperoxia for approximately two weeks (15–16 days) during the prenatal and postnatal periods (HH-2wk), during the prenatal period (HN), or primarily during the postnatal period (NH). The arrow indicates the approximate time of internal pipping (when lung ventilation begins), which usually occurs 1–1.5 days before hatching in this species (Vince and Cheng, 1970). All quail were raised in room air from approximately two weeks of age (31 days after onset of incubation) until studied as adults.

Fig. 2

Ventilatory response to hypoxia (11% O₂) for control quail (NN) and for quail exposed to 60% O₂ during both prenatal and postnatal development (HH-4wk or HH-2wk), during prenatal development only (HN), or during postnatal development (NH); see Fig. 1 for details on the treatment groups. Panels A–E present the increases in respiratory frequency (f_R), tidal volume (V_T), minute ventilation (V̇_E) and ventilation-to-metabolism ratio (V̇_E/V̇_O2 and V̇_E/V̇_CO2) normalized as a percentage increase from baseline. Values are means ± S.E.M., pooled across sexes; n= 52 NN, 31 HH-4wk, 15 HH-2wk, 17 HN and 17 NH. * P<0.05 versus the NN group.

Fig. 3

Ventilatory response to hypoxia (11% O₂) for control quail (NN) and for quail exposed to 60% O₂ during development; see Fig. 1 for details on the treatment groups. In contrast to Figure 2, V̇_E (panel A), V̇_E/V̇_O2 (panel B) and V̇_E/V̇_CO2 (panel C) responses are presented as the increase