Developmental alterations in auditory arousal from sleep in healthy and virus-infected cats

To investigate the impact of respiratory-tract infections on arousability from sleep, we evaluated the auditory arousal responses of healthy and virus-infected cats in two age groups. Arousability was positively associated with stimulus intensity but negatively associated with experimental day. Infected animals were more responsive to auditory stimuli than were uninfected ones, and younger cats were less responsive than older animals. Within the younger groups, infected cats demonstrated increased arousability across the entire range of stimulus volumes during quiet sleep but not during active sleep. Young infected cats also demonstrated lower EEG delta-wave amplitudes than did uninfected animals. These effects on arousability and EEG amplitudes were not observed in older cats. Thus, under the conditions studied, cats with mild viral infections show an age-related enhancement of auditory arousability from sleep, suggesting that they sleep less deeply than do healthy, age-matched animals. The generalization of these observations to other arousing stimuli, such as hypoxia or hypercapnia, and possible implications for the pathogenesis of sudden infant death syndrome remain to be determined.