In conscious rats, disruption of serotonergic neurons in the caudal raphe decreases the ventilatory response to hypercapnia (SFN abstract 221.3, 2002), whereas chronic focal inhibition of serotonin re-uptake here increases the CO2 response (SFN abstract 570.3, 2002). In this study, we determine what role 5HT1A receptors in the caudal raphe play in ventilation during normocapnic and hypercapnic conditions. After surgical instrumentation with microdialysis guide tubes and EEG/EMG electrodes, unanesthetized adult rats were subjected to initial 30-minute microdialysis treatments with artificial cerebrospinal fluid (aCSF) or aCSF containing 1, 10, or 30 mM of the 5HT1A agonist 8-OH-DPAT. Ventilation in room air and in 7% CO2 was then measured in freely-moving animals in a whole body plethysmograph as microdialysis treatment continued. At least 48 hours between dose experiments was allowed for drug wash out. We found that 30 mM 8-OH-DPAT decreased mean tidal volume at 7% CO2 conditions by 21% during wakefulness ...