Role of the pons in hypoxic respiratory depression in the neonatal rat

The main purpose of this study was to evaluate the role of the pens in hypoxic respiratory depression (HRD) of the neonatal rat. Experiments were conducted using the isolated brainstem-spinal cord preparation of the neonatal rat (1-3 days old). The brainstem was transected at various levels. We found that ablation of the diencephalon decreased respiratory frequency (fR), and conversely, that ablation of the midbrain or pens increased fR. In the preparation with the pens intact (without the midbrain), hypoxia (superfusate P-O2 = 56 mmHg) caused strong depression of respiratory activity, which was characterized by a steady decrease in fR and in integrated inspiratory burst amplitude (integral Phr). In the preparation with the intact Ventral pens (without midbrain and dorsal pens) we observed similar, though weaker, HRD. When the entire pens was ablated, integral Phr was little depressed by hypoxia and thus, HRD was further attenuated. We conclude that the pens contributes importantly to the induction of hypoxic respiratory depression in the neonatal rat. Both the ventral and dorsal portions of the pens are involved in the control of hypoxic respiratory depression. In addition, we show that the respiratory modulatory functions of the diencephalon (facilitating) and midbrain (inhibitory) are already expressed at the time of birth. (C) 1998 Elsevier Science B.V.