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Effect of dorsal midbrain lesion in infant rats on development of circadian rhythm
Insights
Neonatal destruction of the dorsal midbrain, including dorsal raphe nuclei, slightly altered circadian rhythms in rats. This suggests the serotonergic system is crucial for normal circadian rhythm development.
Area of Science:
- Neuroscience
- Chronobiology
Background:
- The serotonergic system plays a role in various physiological processes.
- Circadian rhythms regulate daily biological patterns.
Purpose of the Study:
- To investigate the influence of the serotonergic system on the development of circadian rhythms.
- To determine if early-life disruption of the serotonergic system permanently affects circadian regulation.
Main Methods:
- Neonatal rat pups underwent surgical destruction of the dorsal midbrain, including dorsal raphe nuclei.
- Sham-operated pups served as controls.
- Locomotor activity and water consumption patterns were monitored over time.
Main Results:
- Overt circadian rhythms were observed in both groups, but lesioned pups showed increased activity during the light phase.
- Lesioned rats exhibited irregular drinking patterns and a delayed response to light-dark cycle reversals.
- A slight but significant alteration in circadian activity rhythm was noted in lesioned pups.
Conclusions:
- The serotonergic system is involved in the full development of normal circadian rhythms.
- Neonatal dorsal midbrain lesions may induce permanent changes in the mammalian circadian system.
- Disruption of the serotonergic system impacts both activity and drinking rhythms.
Abstract:
To investigate the relationship between serotonergic system and development of the circadian rhythm, we made destruction of the dorsal region of midbrain including dorsal raphe nuclei in neonatal rat pups. Overt circadian rhythms of locomotor activity and water consumption were clearly observed at 4-6 weeks of age, in both the sham operated and the lesioned pups. However, amount of both activities in the lesioned pups was significantly larger than that of the sham operated pups during the light phase. This indicates that the circadian activity rhythm is altered by the lesion, although the degree of alteration is slight. This suggests the involvement of the serotonergic system in the full development of the normal circadian rhythm. An irregular drinking pattern was observed in the lesioned rats at 5 months of age, although a light-dark difference in water consumption was evident. It takes longer for lesioned adult rats to manifest a significant day-night difference in water consumption, than for sham operated rats after reversal of light-dark cycle. This suggests that a lesion in the dorsal midbrain made during the neonatal period may cause a permanent change in the circadian system.