Hypocapnia-dependent facilitation of augmented breaths: Observations in awake vs. anesthetized rats

We investigated whether commonly used injectable laboratory anesthetics alter the regulation of augmented breaths (ABs) in different respiratory backgrounds. Male rats were studied on three separate experimental days, receiving one of three injections in randomized order: ethyl carbamate (‘urethane’; 1.2 mg kg−1), ketamine/xylazine (ket/xyl; 80/10 mg kg−1), or normal saline. Following each of the three interventions, breathing was monitored during 15 min exposures to normoxia (room air), hypoxia (10% O2) and hypoxia + CO2 (10% O2, 5% CO2). Urethane anesthesia completely eliminated ABs from the breathing rhythm in room air conditions (p < 0.001), and decreased the hypocapnia-dependent component of this response (p < 0.001). ket/xyl left the normal incidence of ABs in room air breathing intact but significantly suppressed the hypoxia-induced facilitation of ABs (p = 0.0015). These results provide the first clear evidence that laboratory anesthesia can profoundly alter the regulation of ABs including the hypocapnia-dependent component of their facilitation.

► Injectable anesthetics alter the regulation of augmented breaths (ABs) in rats.
► Urethane prevents their production in normoxic breathing.
► Ketamine/xylazine blunts their facilitation during exposure to hypoxia.
► Under anesthesia hypocapnia remains an essential factor in their facilitation.