E008: Destruction of the locus coeruleus produces ultradian rhythm in spontaneously hypertensive rat

The Locus coeruleus (LC) is an important integrating nucleus in the midbrain, that responds to various internal and external environmental stimuli. It is unclear whether LC has an impact on the magnitude and shape of the circadian variation of BP. Therefore, the purpose of our study was to test the hypothesis whether LC is in involved in the circadian variation of BP. We used ten mature male SHRs (20 ± 11 week old, Body weight, 278 ± 8 g) and ten age-sex matched WKYs (21 ± 11 weeks; Body weight 285 ± 9 g for the control). They were maintained in a thermally controlled (23°C), 12-hour light-cycled (07.00 on 19.00 off) environment and fed lab chow libitum. The Dataquest III system (Data Sciences Inc, St. Paul, Minn) was used to measure telemetrically systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR). The monitoring system consisted of the transmitter, the receiver panel, a consolidation matrix, an IBM-compatible personal computer, and accompanying software. Rats were anesthetized with halothane. The catheter of the sensor was placed in the abdominal aorta. After the rats had recovered completely, 24 hours beat-to-beat monitoring of BP and HR was performed before and after electrolytic LC lesion in a room distant from an acoustic or visual disturbance. Circadian rhythm of blood pressure was analyzed using maximum entropy methods (MEM). The results are presented as the mean one standard error of the mean. Conventional statistics were used. Probability levels of less than 0.05 were considered significant. 24 hours mean SBP and DBP were higher in SHR than WKY. The BP in SHR and WKY did not change after LC lesion. The SBP was still higher in SHR than WKY. HR did not differ between SHR and WKY, and between before and after LC lesion. The first peak frequency of power density was 0.041 1/hour, which is 24.2 hour. After LC lesion, the first peak of BP became smaller and many short peaks of lower and higher frequencies appeared (12 hour, 8 hour and 6 hour length). However, the periodicity of the first peak did not change either in SHR BP between before and after LC lesion or in WKY BP between before and after LC lesion. The relative height of first peak of frequency in SBP and DBP became shorter after LC lesion. The power spectral density of SBP in both SHR and WKY showed 1/f characteristics. The slope of 1/f in both SBP and DBP did not differ between before and after LC lesion. The important findings of our studies are: LC lesion seem