Serotonin-containing neurons within the medullary raphe are activated as a result of hypoxia, and non-specific lesions of this area increases the ventilatory response to 7% O2 in unanesthetized rats. We found that microdialysis of the 5HT1A agonist R(+)-8-hydroxy-2(di-n-propylamino)tetralin (DPAT) into the medullary raphe decreases the ventilatory response to hypercapnia in conscious rats (SFN abstract 826.6, 2003). Here we ask whether decreasing serotonergic activity in the medullary raphe by microdialysis of DPAT affects the ventilatory response to hypoxia. Eight adult rats were surgically implanted with EEG/EMG electrodes, abdominal temperature probes, and microdialysis guide tubes in the medullary raphe. Following recovery, rats were microdialyzed on separate days with either artificial cerebrospinal fluid (aCSF) or 30 mM DPAT throughout the protocol beginning 30 minutes before the onset of recording. We measured ventilation (whole body plethysmography) during room air (30 min), 10% O2 (1 hr), and reco...