Changes in sleep patterns in spontaneously hypertensive rats

Study Objectives: To explore whether spontaneous hypertension is associated with a change in sleep pattern in rats. Design: Adult male spontaneously hypertensive rats (SHR) were compared to normotensive Wistar-Kyoto rats (WKY) on their normal daytime sleep pattern. Participants: Ten WKY and 10 SHR. Interventions: All rats had electrodes implanted for polygraphic recordings. Weeks later, a 5-hour daytime sleep-weakfulness recording session was analyzed. Measurements and Results: Electroencephalogram and electromyogram signals were subjected to continuous power spectral analysis, from which mean power frequency of the electroencephalogram and power of the electromyogram were quantified. Active waking (AW), quiet sleep (QS), and paradoxical sleep (PS) were defined every 8 seconds from corresponding mean power frequency and electromyogram power readings. Analysis of heart-rate variability was derived from the electrocardiogram signals. Macrostructural analysis of sleep revealed that SHR were characterized by fewer QS and PS episodes and eventually shorter accumulated QS and PS times as compared to WKY. SHR also had more QS-to-AW transitions but fewer QS-to-PS transitions. Microstructural analysis revealed that SHR were associated with more-frequent interruptions during QS. Analysis of heart-rate variability indicated that SHR had similar R-R intervals and lower high-frequency (0.6-2.4 Hz) power but a higher ratio of low-frequency (0.06-0.6 Hz) power to high-frequency power during the daytime recording as compared to WKY. Conclusions: As compared to WKY, SHR may have less sleep time, poorer sleep quality, and a greater tendency to wake up from QS. Such changes in sleep may be concomitant with cardiac autonomic changes. Our methodology offers a convenient yet effective way to study the constitution, sequence, and interruption of sleep in the rat.