Effect of neonatal anoxia on the ventilatory response to hypoxia in developing rats

The purpose of the study was to determine whether an episode of anoxia in the neonatal period affects the hypoxic ventilatory response in developing rats. Three to 4 day old rats (EXP rats) (day 0 = day of birth) were exposed to 100% N(2) for about 20 min. In anoxia, animals changed their respiratory movements to "gasping," and were successfully autoresuscitated by placing them back into air. None of the EXP rats died after the resuscitation, and no differences were found between the EXP and control (CONT) rats in the somatic growth. The CONT rats were not exposed to anoxia during the neonatal period. On day 9-10(mean day 9) and days 23-29(mean day 25), ventilatory and metabolic responses to hypoxia (inspiratory oxygen fraction F(i)O(2 )= 10% on day 9; 15% and 10% on day 25) were compared in the EXP and CONT groups. On day 9, there were no differences in ventilatory and metabolic responses to hypoxia between the EXP and CONT groups. On day 25, 10% O(2)hypoxic ventilatory response (by the barometric method) was significantly higher in the EXP group than in the CONT group, as indicated by increases in both tidal volume (V(T)) and mean inspiratory flow (V(T)/T(I)). On the other hand, the metabolic effects were small, because metabolic rates (V'O(2) and V'CO(2), by a flow-through method) were similar in both EXP and CONT groups under each gaseous condition. These results suggest that an episode of anoxia during the neonatal period has long-lasting effects on the control of ventilation, including chemoreflexes, in rats.