ROLE OF THE PARABRACHIAL NUCLEUS IN VENTILATORY RESPONSES OF AWAKE RATS

1. The parabrachial nucleus (PBN) is thought to play an important role in cardiorespiratory control. However, the circumstances under which it affects ventilation are still not known. The purpose of the present study was to investigate how the PBN modulates the ventilatory respon ses to hypercapnia, hypoxia or a resistive load in awake rats with che mical lesions of the PBN. 2. In three groups of rats (with lateral PBN lesion, with Kolliker-Fuse nucleus lesion and control), ventilation w as measured under various conditions. 3. There was no difference in th e breathing of normal room air in any of the groups. However, the lesi oned groups showed a reduced ventilatory response to hyperoxic hyperca pnia (inspired CO2 fractions (F-I,F-CO2) of 3, 5, 8 and 10%) and to gr aded hypoxia (inspired O-2 fractions (F-I,F-O2) of 16, 12, 10 and 8%) compared with the control group. The control group showed a biphasic r esponse to sustained hypoxia (F-I,F-O2 at 10% for 30 min), known as 'h ypoxic depression', while the lesioned groups showed moderate ventilat ory exaggeration throughout hypoxia. In response to a resistive load, the lateral PBN lesion group showed no change in ventilatory compensat ion. 4. The PBN appeared to have a considerable influence on ventilati on stimulated in various ways during wakefulness.