Behavioural correlates of conditioned ventilatory responses to hypoxia in rats

To examine the possible contribution of behavioural arousal to ventilatory conditioning, we performed a differential conditioning experiment using two odours as the paired conditioned stimulus (CS +) and unpaired conditioned stimulus (CS -) and a hypoxic mixture (7.5% O-2) as the unconditioned stimu lus (US) in 24 adult male rats. Vanillin was the CS + and rose the CS - in half the rats, and vice versa in the other half. Each rat underwent 26 pair ed CS + /hypoxia trials and 26 CS - trials in alternation, followed by two CS + only and two CS - trials to test for conditioning. Analysis of breathi ng variables and behavioural scores during the test showed two qualitativel y different conditioned responses. The initial conditioned response was cha racterised by short breath durations (TT), frequent sniffing episodes, and arousal responses. Following this, a specific, conditioned increase in tida l volume (VT) and levelling off of sniffing and motor activities occurred. The early TT-response and late VT-response to CS + both contributed to an i ncrease in ventilation (VI). The present data show that the association of an odour and hypoxia elicits a biphasic ventilatory conditioned response, o f which the first component is integrated into conditioned arousal. (C) 199 9 Elsevier Science B.V. All rights reserved.