|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1994 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1993 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1992 : ¥800,000 (Direct Cost : ¥800,000)
In the present study we investigated effects of stress on the circadian activity rhythms and NA turnover in rat brain regions. Male Wistar rats were used as subjects. After a stable free-running was obtained, the animals were exposed to stress with a wire mesh for 60 min at six circadian time (CT) points (CT2, CT6CT10, CT14、CT18, CT22). The levels of the major metabolite of NA in the rat brain, MHPG-SO4, were determined by the fluorometric method. Phase advances were observed at CT2, CT6, CT18 and CT22 with the maximum phase advance at CT22 and phase delay were observed at CT10. No phase-shifts was found at between CT14 and CT18. These results suggest that stress produces phase-shifts in the circadian activity rhythm, of which magnitude and direction were dependent upon the CT when the stress was given. The levels of MHPG-SO4 in non-stressed control animals exhibited no significant differences at among all CT points, did not show the circadian variation. The stress caused significant i
ncreases in the MHPG-SO4 levels at all CT points examined as compared to the respective controls. Moreover, the stress-induced increases in the MHPG-SO4 levels were significantly higher at both CT10 and CT22 than when exposed to the stress at other CT points.
These results suggest that even if the same duration of stress was given to animals, the magnitude of responses of NA neurons was different depending on the time when the stress was given. In the present study, it is noteworthy that the maximum phase advance and phase delay induced by stress occurred at CT10 and CT22 when the stress caused more marked enhancement of NA turnover in the LC region.It has been reported that enhancement of NA turnover in the LC region was associated with arousal ; that is, the LC is thought to make raising the arousal levels in mammals. Moreover, the levels of arousal and/or excitement of an organism have a feedback effect on the circadian clock. Therefore, the stress-induced phase-shifting effects seems to be related to the changes of arousal levels. Moreover, we speculate that the changes in NA turnover in the LC region induced by stress might cause the changes in the phase through a feedback mechanism of the arousal (activity levels) on the circadian clock. Less