ROLE OF THE PENS 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 o f the neonatal rat (1-3 days old). The brainstem was transected at var ious levels. We found that ablation of the diencephalon decreased resp iratory 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 dep ression of respiratory activity, which was characterized by a steady d ecrease in fR and in integrated inspiratory burst amplitude (integral Phr). In the preparation with the intact Ventral pens (without midbrai n and dorsal pens) we observed similar, though weaker, HRD. When the e ntire pens was ablated, integral Phr was little depressed by hypoxia a nd thus, HRD was further attenuated. We conclude that the pens contrib utes importantly to the induction of hypoxic respiratory depression in the neonatal rat. Both the ventral and dorsal portions of the pens ar e involved in the control of hypoxic respiratory depression. In additi on, we show that the respiratory modulatory functions of the diencepha lon (facilitating) and midbrain (inhibitory) are already expressed at the time of birth. (C) 1998 Elsevier Science B.V.